```
# Service workers
Service Worker は、アプリ内部でネットワークリクエストを処理するプロキシサーバーとして機能します。これによりアプリをオフラインで動作させることが可能になります。もしオフラインサポートが不要な場合（または構築するアプリの種類によって現実的に実装できない場合）でも、ビルドした JS と CSS を事前にキャッシュしてナビゲーションを高速化するために Service Worker を使用する価値はあります。
In SvelteKit, if you have a `src/service-worker.js` file (or `src/service-worker/index.js`) it will be bundled and automatically registered.
service worker を独自のロジックで登録する必要がある場合や、その他のソリューションを使う場合は、[自動登録を無効化](configuration#serviceWorker) することができます。デフォルトの登録方法は次のようなものです:
```js
if ('serviceWorker' in navigator) {
addEventListener('load', function () {
navigator.serviceWorker.register('./path/to/service-worker.js');
});
}
```
## service worker の内部では
service worker の内部では、[`$service-worker` モジュール]($service-worker) にアクセスでき、これによって全ての静的なアセット、ビルドファイル、プリレンダリングページへのパスが提供されます。また、アプリのバージョン文字列 (一意なキャッシュ名を作成するのに使用できます) と、デプロイメントの `base` パスが提供されます。Vite の設定に `define` (グローバル変数の置換に使用) を指定している場合、それはサーバー/クライアントのビルドだけでなく、service worker にも適用されます。
次の例では、ビルドされたアプリと `static` にあるファイルをすぐに(eagerly)キャッシュし、その他全てのリクエストはそれらの発生時にキャッシュします。これにより、各ページは一度アクセスするとオフラインで動作するようになります。
```js
/// file: src/service-worker.js
// Disables access to DOM typings like `HTMLElement` which are not available
// inside a service worker and instantiates the correct globals
///
///
///
// Ensures that the `$service-worker` import has proper type definitions
///
// Only necessary if you have an import from `$env/static/public`
///
import { build, files, version } from '$service-worker';
// This gives `self` the correct types
const self = /** @type {ServiceWorkerGlobalScope} */ (/** @type {unknown} */ (globalThis.self));
// Create a unique cache name for this deployment
const CACHE = `cache-${version}`;
const ASSETS = [
...build, // the app itself
...files // everything in `static`
];
self.addEventListener('install', (event) => {
// Create a new cache and add all files to it
async function addFilesToCache() {
const cache = await caches.open(CACHE);
await cache.addAll(ASSETS);
}
event.waitUntil(addFilesToCache());
});
self.addEventListener('activate', (event) => {
// Remove previous cached data from disk
async function deleteOldCaches() {
for (const key of await caches.keys()) {
if (key !== CACHE) await caches.delete(key);
}
}
event.waitUntil(deleteOldCaches());
});
self.addEventListener('fetch', (event) => {
// ignore POST requests etc
if (event.request.method !== 'GET') return;
async function respond() {
const url = new URL(event.request.url);
const cache = await caches.open(CACHE);
// `build`/`files` can always be served from the cache
if (ASSETS.includes(url.pathname)) {
const response = await cache.match(url.pathname);
if (response) {
return response;
}
}
// for everything else, try the network first, but
// fall back to the cache if we're offline
try {
const response = await fetch(event.request);
// if we're offline, fetch can return a value that is not a Response
// instead of throwing - and we can't pass this non-Response to respondWith
if (!(response instanceof Response)) {
throw new Error('invalid response from fetch');
}
if (response.status === 200 && !response.headers.get('cache-control')?.includes('no-store')) {
cache.put(event.request, response.clone());
}
return response;
} catch (err) {
const response = await cache.match(event.request);
if (response) {
return response;
}
// if there's no cache, then just error out
// as there is nothing we can do to respond to this request
throw err;
}
}
event.respondWith(respond());
});
```
> [!NOTE] キャッシュにはご注意ください！ 場合によっては、オフラインでは利用できないデータよりも古くなったデータのほうが悪いことがあります。ブラウザはキャッシュが一杯になると空にするため、ビデオファイルのような大きなアセットをキャッシュする場合にもご注意ください。
## 開発中は(During development)
service worker はプロダクション向けにはバンドルされますが、開発中はバンドルされません。そのため、[modules in service workers](https://web.dev/es-modules-in-sw) をサポートするブラウザのみ、開発時にもそれを使用することができます。service worker を手動で登録する場合、開発時に `{ type: 'module' }` オプションを渡す必要があります:
```js
import { dev } from '$app/environment';
navigator.serviceWorker.register('/service-worker.js', {
type: dev ? 'module' : 'classic'
});
```
> [!NOTE] `build` と `prerendered` は開発中は空配列です
## その他のソリューション
SvelteKit の service worker 実装は、簡単に動作するように設計されており、ほとんどのユーザーにとって良いソリューションでしょう。しかし、SvelteKit 以外の多くの PWA アプリケーションは [Workbox](https://web.dev/learn/pwa/workbox) というライブラリを活用しています。Workbox に慣れている方は [Vite PWA plugin](https://vite-pwa-org.netlify.app/frameworks/sveltekit.html) の方が好まれるかもしれません。
## References
For more general information on service workers, we recommend [the MDN web docs](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers).
# Server-only modules
良き友人のように、SvelteKit はあなたの秘密を守ります。バックエンドとフロントエンドが同じリポジトリにある場合、機密データをフロントエンドのコードに誤ってインポートしてしまうことが簡単に起こってしまいます (例えば、API キーを持つ環境変数など)。SvelteKit はこれを完全に防ぐ方法を提供します: サーバー専用のモジュール(server-only modules)です
## Private environment variables
[`$env/static/private`]($env-static-private) モジュールと [`$env/dynamic/private`]($env-dynamic-private) モジュールは、[`hooks.server.js`](hooks#Server-hooks) や [`+page.server.js`](routing#page-page.server.js) のようなサーバー上でのみ実行されるモジュールにのみインポートすることが可能です。
## Server-only utilities
The [`$app/server`]($app-server) module, which contains a [`read`]($app-server#read) function for reading assets from the filesystem, can likewise only be imported by code that runs on the server.
## Your modules
モジュールをサーバー専用にするには2通りの方法があります:
- ファイル名に `.server` を付けます。例: `secrets.server.js`
- モジュールを `$lib/server` に置きます。例: `$lib/server/secrets.js`
## How it works
パブリックに公開されるコード (public-facing code) にサーバー専用のコードを (直接的かまたは間接的かにかかわらず) インポートすると…
```js
// @errors: 7005
/// file: $lib/server/secrets.js
export const atlantisCoordinates = [/* redacted */];
```
```js
// @errors: 2307 7006 7005
/// file: src/routes/utils.js
export { atlantisCoordinates } from '$lib/server/secrets.js';
export const add = (a, b) => a + b;
```
```html
/// file: src/routes/+page.svelte
```
…SvelteKit はエラーとなります:
```
Cannot import $lib/server/secrets.ts into code that runs in the browser, as this could leak sensitive information.
src/routes/+page.svelte imports
src/routes/utils.js imports
$lib/server/secrets.ts
If you're only using the import as a type, change it to `import type`.
```
パブリックに公開されるコード `src/routes/+page.svelte` は、`add` を使用しているのみで、シークレットの `atlantisCoordinates` を使用していませんが、ブラウザがダウンロードする JavaScript にシークレットなコードが残ってしまう可能性があり、このインポートチェーンは安全ではないと考えられます。
この機能は動的なインポート(dynamic imports)でも動作し、``await import(`./${foo}.js`)`` のような補完されたインポートに対しても有効です。
> [!NOTE] Vitest のようなユニットテストフレームワークはサーバー専用のコードと公開されるコードを区別しません。そのため、テストの実行中、つまり `process.env.TEST === 'true'` となっているときは、不正なインポートの検出は無効化されます。
## その他の参考資料
- [Tutorial: Environment variables](/tutorial/kit/env-static-private)
# Snapshots
例えばサイドバーのスクロールポジションや、`
` 要素の中身などの、一時的な DOM の状態(state)は、あるページから別のページに移動するときに破棄されます。
例えば、ユーザーがフォームに入力し、それを送信する前に別のページに移動してからまた戻ってきた場合や、ページをリフレッシュした場合、フォームに入力されていた値は失われます。入力内容を保持しておくことが重要な場合、DOM の状態を _スナップショット(snapshot)_ として記録することができ、ユーザーが戻ってきたときに復元することができます。
これを行うには、`+page.svelte` や `+layout.svelte` で、`capture` メソッドと `restore` メソッドを持つ `snapshot` オブジェクトをエクスポートします:
```svelte
```
このページから離れるとき、ページが更新される直前に `capture` 関数が呼ばれ、戻り値がブラウザの history スタックの現在のエントリーに関連付けられます。もしこのページに戻ってきた場合、ページが更新されるとすぐに保存された値とともに `restore` 関数が呼ばれます。
データは `sessionStorage` に永続化できるように、JSON としてシリアライズ可能でなければなりません。これにより、ページがリロードされたときや、ユーザーが別のサイトから戻ってきたときにも、状態を復元することができます。
> [!NOTE] 大きすぎるオブジェクトを `capture` から返さないようにしてください。一度 capture されたオブジェクトは、そのセッションの間はメモリ上に保持されるので、極端な場合には、大きすぎて `sessionStorage` に永続化できない可能性があります。
# Shallow routing
As you navigate around a SvelteKit app, you create _history entries_. Clicking the back and forward buttons traverses through this list of entries, re-running any `load` functions and replacing page components as necessary.
Sometimes, it's useful to create history entries _without_ navigating. For example, you might want to show a modal dialog that the user can dismiss by navigating back. This is particularly valuable on mobile devices, where swipe gestures are often more natural than interacting directly with the UI. In these cases, a modal that is _not_ associated with a history entry can be a source of frustration, as a user may swipe backwards in an attempt to dismiss it and find themselves on the wrong page.
SvelteKit makes this possible with the [`pushState`]($app-navigation#pushState) and [`replaceState`]($app-navigation#replaceState) functions, which allow you to associate state with a history entry without navigating. For example, to implement a history-driven modal:
```svelte
{#if page.state.showModal}
history.back()} />
{/if}
```
The modal can be dismissed by navigating back (unsetting `page.state.showModal`) or by interacting with it in a way that causes the `close` callback to run, which will navigate back programmatically.
## API
The first argument to `pushState` is the URL, relative to the current URL. To stay on the current URL, use `''`.
The second argument is the new page state, which can be accessed via the [page object]($app-state#page) as `page.state`. You can make page state type-safe by declaring an [`App.PageState`](types#PageState) interface (usually in `src/app.d.ts`).
To set page state without creating a new history entry, use `replaceState` instead of `pushState`.
> [!LEGACY]
> `page.state` from `$app/state` was added in SvelteKit 2.12. If you're using an earlier version or are using Svelte 4, use `$page.state` from `$app/stores` instead.
## Loading data for a route
When shallow routing, you may want to render another `+page.svelte` inside the current page. For example, clicking on a photo thumbnail could pop up the detail view without navigating to the photo page.
For this to work, you need to load the data that the `+page.svelte` expects. A convenient way to do this is to use [`preloadData`]($app-navigation#preloadData) inside the `click` handler of an `` element. If the element (or a parent) uses [`data-sveltekit-preload-data`](link-options#data-sveltekit-preload-data), the data will have already been requested, and `preloadData` will reuse that request.
```svelte
{#each data.thumbnails as thumbnail}
{
if (innerWidth < 640 // bail if the screen is too small
|| e.shiftKey // or the link is opened in a new window
|| e.metaKey || e.ctrlKey // or a new tab (mac: metaKey, win/linux: ctrlKey)
// should also consider clicking with a mouse scroll wheel
) return;
// prevent navigation
e.preventDefault();
const { href } = e.currentTarget;
// run `load` functions (or rather, get the result of the `load` functions
// that are already running because of `data-sveltekit-preload-data`)
const result = await preloadData(href);
if (result.type === 'loaded' && result.status === 200) {
pushState(href, { selected: result.data });
} else {
// something bad happened! try navigating
goto(href);
}
}}
>
{/each}
{#if page.state.selected}
history.back()}>
{/if}
```
## Caveats
During server-side rendering, `page.state` is always an empty object. The same is true for the first page the user lands on — if the user reloads the page (or returns from another document), state will _not_ be applied until they navigate.
Shallow routing is a feature that requires JavaScript to work. Be mindful when using it and try to think of sensible fallback behavior in case JavaScript isn't available.
# Observability
Available since 2.31
Sometimes, you may need to observe how your application is behaving in order to improve performance or find the root cause of a pesky bug. To help with this, SvelteKit can emit server-side [OpenTelemetry](https://opentelemetry.io) spans for the following:
- The [`handle`](hooks#Server-hooks-handle) hook and `handle` functions running in a [`sequence`](@sveltejs-kit-hooks#sequence) (these will show up as children of each other and the root `handle` hook)
- Server [`load`](load) functions and universal `load` functions when they're run on the server
- [Form actions](form-actions)
- [Remote functions](remote-functions)
Just telling SvelteKit to emit spans won't get you far, though — you need to actually collect them somewhere to be able to view them. SvelteKit provides `src/instrumentation.server.ts` as a place to write your tracing setup and instrumentation code. It's guaranteed to be run prior to your application code being imported, providing your deployment platform supports it and your adapter is aware of it.
Both of these features are currently experimental, meaning they are likely to contain bugs and are subject to change without notice. You must opt in by adding the `kit.experimental.tracing.server` and `kit.experimental.instrumentation.server` option in your `svelte.config.js`:
```js
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
experimental: {
+++tracing: {
server: true
},
instrumentation: {
server: true
}+++
}
}
};
export default config;
```
> [!NOTE] Tracing — and more significantly, observability instrumentation — can have a nontrivial overhead. Before you go all-in on tracing, consider whether or not you really need it, or if it might be more appropriate to turn it on in development and preview environments only.
## Augmenting the built-in tracing
SvelteKit provides access to the `root` span and the `current` span on the request event. The root span is the one associated with your root `handle` function, and the current span could be associated with `handle`, `load`, a form action, or a remote function, depending on the context. You can annotate these spans with any attributes you wish to record:
```js
/// file: $lib/authenticate.ts
// @filename: ambient.d.ts
declare module '$lib/auth-core' {
export function getAuthenticatedUser(): Promise<{ id: string }>
}
// @filename: index.js
// ---cut---
import { getRequestEvent } from '$app/server';
import { getAuthenticatedUser } from '$lib/auth-core';
async function authenticate() {
const user = await getAuthenticatedUser();
const event = getRequestEvent();
event.tracing.root.setAttribute('userId', user.id);
}
```
## Development quickstart
To view your first trace, you'll need to set up a local collector. We'll use [Jaeger](https://www.jaegertracing.io/docs/getting-started/) in this example, as they provide an easy-to-use quickstart command. Once your collector is running locally:
- Turn on the experimental flags mentioned earlier in your `svelte.config.js` file
- Use your package manager to install the dependencies you'll need:
```sh
npm i @opentelemetry/sdk-node @opentelemetry/auto-instrumentations-node @opentelemetry/exporter-trace-otlp-proto import-in-the-middle
```
- Create `src/instrumentation.server.js` with the following:
```js
// @errors: 2307
/// file: src/instrumentation.server.js
import { NodeSDK } from '@opentelemetry/sdk-node';
import { getNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node';
import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-proto';
import { createAddHookMessageChannel } from 'import-in-the-middle';
import { register } from 'node:module';
const { registerOptions } = createAddHookMessageChannel();
register('import-in-the-middle/hook.mjs', import.meta.url, registerOptions);
const sdk = new NodeSDK({
serviceName: 'test-sveltekit-tracing',
traceExporter: new OTLPTraceExporter(),
instrumentations: [getNodeAutoInstrumentations()]
});
sdk.start();
```
Now, server-side requests will begin generating traces, which you can view in Jaeger's web console at [localhost:16686](http://localhost:16686).
## `@opentelemetry/api`
SvelteKit uses `@opentelemetry/api` to generate its spans. This is declared as an optional peer dependency so that users not needing traces see no impact on install size or runtime performance. In most cases, if you're configuring your application to collect SvelteKit's spans, you'll end up installing a library like `@opentelemetry/sdk-node` or `@vercel/otel`, which in turn depend on `@opentelemetry/api`, which will satisfy SvelteKit's dependency as well. If you see an error from SvelteKit telling you it can't find `@opentelemetry/api`, it may just be because you haven't set up your trace collection yet. If you _have_ done that and are still seeing the error, you can install `@opentelemetry/api` yourself.
# Packaging
SvelteKit では、アプリを構築するだけでなく、`@sveltejs/package` パッケージを使用してコンポーネントライブラリを構築することもできます (`npx sv create` にはこれを設定するためのオプションがあります)。
アプリを作成するとき、`src/routes` のコンテンツが公開される部分となります。[`src/lib`]($lib) にはアプリの内部ライブラリが含まれます。
コンポーネントライブラリは SvelteKit アプリと同じ構造ですが、`src/lib` が公開される部分である点が異なります。パッケージの公開にはプロジェクトの最上位(root)の `package.json` が使用されます。`src/routes` を、ライブラリに付属するドキュメントやデモサイト、または開発中に使用するサンドボックスにすることもあるでしょう。
`@sveltejs/package` の `svelte-package` コマンドを実行すると、`src/lib` の中身を取り込み、以下を含む `dist` ([設定で変更](#Options)できます) ディレクトリを生成します:
- `src/lib` にある全てのファイル。Svelte コンポーネントはプリプロセスされ、TypeScript ファイルは JavaScript にトランスパイルされます。
- Svelte、JavaScript、TypeScript ファイル向けに生成される型定義 (`d.ts` ファイル)。このために、`typescript >= 4.0.0` をインストールする必要があります。型定義はその実装と同じ場所に配置され、手書きの `d.ts` ファイルはそのままコピーされます。[生成を無効](#Options)にすることもできますが、それはおすすめできません。あなたのライブラリを使用する人は TypeScript を使用しているかもしれません。その場合、この型定義ファイルが必要になります。
> [!NOTE] `@sveltejs/package` バージョン1は `package.json` を生成していましたが、この仕様は変更され、現在はプロジェクトの `package.json` を使用しそれが正しいか検証するようになりました。もしまだバージョン1を使用している場合は、[この PR](https://github.com/sveltejs/kit/pull/8922) にある移行手順(Migration instructions)をご覧ください。
## package.json の構造
公開するライブラリをビルドするのであれば、`package.json` の内容がとても重要になります。これを通して、パッケージのエントリーポイントや、どのファイルを npm に公開するか、そしてあなたのライブラリの依存関係を設定することができます。それでは、重要なフィールドをひとつずつ見ていきましょう。
### name
これはパッケージの名前です。他の人はこの名前を使用してインストールすることになります。そして `https://npmjs.com/package/` のように表示されるようになります。
```json
{
"name": "your-library"
}
```
詳細については[こちら](https://docs.npmjs.com/cli/v9/configuring-npm/package-json#name)をお読みください。
### license
すべてのパッケージにはライセンスフィールドがあるべきです。なぜなら、人々はこれによってどのように使用することが許可されているのか知ることができるからです。配布や保証なしの再利用に関してとても寛容で、非常にポピュラーなライセンスとして、`MIT` があります。
```json
{
"license": "MIT"
}
```
詳細については[こちら](https://docs.npmjs.com/cli/v9/configuring-npm/package-json#license)をお読みください。`LICENSE` ファイルもパッケージに含めるとよいでしょう。
### files
ここではどのファイルを npm にアップロードするかを設定します。出力先フォルダ (デフォルトは `dist`) も含める必要があります。`package.json` と `README` と `LICENSE` は常に含まれるようになっているため、指定する必要はありません。
```json
{
"files": ["dist"]
}
```
不要なファイル (例えば単体テストや、`src/routes` からのみインポートされているモジュールなど) を除外するには、`.npmignore` ファイルにそれらを追加します。これによってより小さいパッケージとなり、インストールも速くなります。
詳細については[こちら](https://docs.npmjs.com/cli/v9/configuring-npm/package-json#files)をお読みください。
### exports
`"exports"` フィールドにはパッケージのエントリーポイントを含めます。`npx sv create` を使用して新しいライブラリプロジェクトをセットアップした場合、単一の export として、パッケージの最上位(root)が設定されています:
```json
{
"exports": {
".": {
"types": "./dist/index.d.ts",
"svelte": "./dist/index.js"
}
}
}
```
これにより、あなたのパッケージにはエントリーポイントが1つだけで、それは最上位(root)で、(以下のように)すべてここを通してインポートされるべきである、ということをバンドラーやツール類に伝えます:
```js
// @errors: 2307
import { Something } from 'your-library';
```
`types` と `svelte` キーは [export conditions](https://nodejs.org/api/packages.html#conditional-exports) です。これはツール類に、`your-library` インポートを検索する際にどのファイルをインポートするかを伝えるものです:
- TypeScript は `types` condition を見て、型定義ファイルを検索します。型定義を公開しない場合は、この condition を省略します。
- Svelte を認識するツール類は `svelte` condition を見て、これが Svelte コンポーネントライブラリであることを認識します。Svelte コンポーネントをエクスポートせず、Svelte 以外のプロジェクトでも使用できるライブラリ (例えば Svelte store ライブラリ) を公開する場合、この condition を `default` に置き換えることができます。
> [!NOTE] 以前のバージョンの `@sveltejs/package` は `package.json` export も追加していましたが、現在は違います。すべてのツール類が明示的にエクスポートされていない `package.json` を扱うことができるようになったからです。
`exports` を好みに合わせて調整し、より多くのエントリーポイントを提供することができます。例えば、コンポーネントを再エクスポートする `src/lib/index.js` ファイルの代わりに、`src/lib/Foo.svelte` コンポーネントを直接公開したい場合、以下のような export map を作成できます…
```json
{
"exports": {
"./Foo.svelte": {
"types": "./dist/Foo.svelte.d.ts",
"svelte": "./dist/Foo.svelte"
}
}
}
```
…そしてライブラリの使用者はコンポーネントをこのようにインポートできます:
```js
// @filename: ambient.d.ts
declare module 'your-library/Foo.svelte';
// @filename: index.js
// ---cut---
import Foo from 'your-library/Foo.svelte';
```
> [!NOTE] 型定義を提供している場合、これを行う際にさらなる注意が必要となることにお気をつけください。注意事項については[こちら](#TypeScript)をお読みください。
一般的に、exports map の各キーはユーザーがあなたのパッケージからなにかインポートするときに使用すべきパスであり、その値はインポートされるファイルへのパスか、またはそのファイルパスを含む export condition の map です。
`exports` の詳細については[こちら](https://nodejs.org/docs/latest-v18.x/api/packages.html#package-entry-points)をお読みください。
### svelte
これはツール類に Svelte コンポーネントライブラリを認識できるようにするレガシーなフィールドです。`svelte` [export condition](#Anatomy-of-a-package.json-exports) を使用している場合は必要ありませんが、まだ export condition を認識しない古いツールとの後方互換性のために残しておくとよいでしょう。あなたの最上位(root)のエントリーポイントを指しているはずです。
```json
{
"svelte": "./dist/index.js"
}
```
### sideEffects
The `sideEffects` field in `package.json` is used by bundlers to determine if a module may contain code that has side effects. A module is considered to have side effects if it makes changes that are observable from other scripts outside the module when it's imported. For example, side effects include modifying global variables or the prototype of built-in JavaScript objects. Because a side effect could potentially affect the behavior of other parts of the application, these files/modules will be included in the final bundle regardless of whether their exports are used in the application. It is a best practice to avoid side effects in your code.
Setting the `sideEffects` field in `package.json` can help the bundler to be more aggressive in eliminating unused exports from the final bundle, a process known as tree-shaking. This results in smaller and more efficient bundles. Different bundlers handle `sideEffects` in various manners. While not necessary for Vite, we recommend that libraries state that all CSS files have side effects so that your library will be [compatible with webpack](https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free). This is the configuration that comes with newly created projects:
```json
/// file: package.json
{
"sideEffects": ["**/*.css"]
}
```
> [!NOTE] If the scripts in your library have side effects, ensure that you update the `sideEffects` field. All scripts are marked as side effect free by default in newly created projects. If a file with side effects is incorrectly marked as having no side effects, it can result in broken functionality.
If your package has files with side effects, you can specify them in an array:
```json
/// file: package.json
{
"sideEffects": [
"**/*.css",
"./dist/sideEffectfulFile.js"
]
}
```
This will treat only the specified files as having side effects.
## TypeScript
あなたが TypeScript を使用していないとしても、あなたのライブラリの型定義を公開したほうがよいでしょう。あなたのライブラリを使用する人が、適切なインテリセンスを得られるようになるからです。`@sveltejs/package` は型生成のプロセスをほとんど隠ぺい(opaque)してくれます。デフォルトでは、ライブラリをパッケージングする際、JavaScript、TypeScript、Svelte ファイル向けに型定義を自動生成します。あなたは [exports](#Anatomy-of-a-package.json-exports) map の `types` condition が正しいファイルを指しているか確認するだけです。`npx sv create` でライブラリプロジェクトを初期化すると、root export に `types` condition が設定されます。
しかし、root export 以外のもの、例えば `your-library/foo` インポートを提供する場合などは、型定義を提供する上でさらなる注意が必要です。残念ながら、TypeScript はデフォルトでは `{ "./foo": { "types": "./dist/foo.d.ts", ... }}` のような export に対して `types` condition を解決しません。代わりに、ライブラリの root からの相対で `foo.d.ts` を探します (つまり、`your-library/dist/foo.d.ts` ではなく `your-library/foo.d.ts` です)。これを修正する方法として、選択肢が2つあります:
1つ目の選択肢は、あなたのライブラリを使用する人に対し、`tsconfig.json` (または `jsconfig.json`) の `moduleResolution` オプション に `bundler` (TypeScript 5 から利用可能で、将来的にもベストかつ推奨のオプション) か `node16` か `nodenext` を設定してもらうように要求することです。これによって TypeScript が実際に exports map を見て正しく型を解決してくれるようになります。
2つ目の選択肢は、TypeScript の `typesVersions` 機能を使用(乱用)して、型を紐付けます。これは、TypeScript が TypeScript のバージョンによって異なる型定義をチェックするために使用している `package.json` 内のフィールドで、このためにパスマッピング機能があります。このパスマッピング機能を利用して、やりたいことを実現できます。上述の `foo` export の場合、対応する `typesVersions` はこのようになります:
```json
{
"exports": {
"./foo": {
"types": "./dist/foo.d.ts",
"svelte": "./dist/foo.js"
}
},
"typesVersions": {
">4.0": {
"foo": ["./dist/foo.d.ts"]
}
}
}
```
`>4.0` は、TypeScript のバージョンが 4 より大きい場合、内側の map をチェックするよう TypeScript に伝えるものです (実際には常に true となるべきものです)。内側の map は TypeScript に `your-library/foo` に対する型付けが `./dist/foo.d.ts` にあることを伝えるためのもので、実質 `exports` condition を置き換えています。また、ワイルドカードとして `*` を自由に使用できるので、同じことを繰り返すことなくたくさんの型定義を一度で使用可能にすることができます。もし `typesVersions` を選択した場合、(`"index.d.ts": [..]` と定義されている) root import を含む全ての型のインポートを、これを通して宣言しなければならないことにご注意ください。
この機能についてより詳しい情報は[こちら](https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html#version-selection-with-typesversions)でお読み頂けます。
## ベストプラクティス
他の SvelteKit プロジェクトからのみ使用されることを想定しているのでなければ、`$app/environment` などの SvelteKit 固有のモジュールをあなたのパッケージで使用するのは避けたほうがよいでしょう。例えば、`import { browser } from '$app/environment'` を使用するのではなく、`import { BROWSER } from 'esm-env'` ([esm-env ドキュメント参照](https://github.com/benmccann/esm-env)) を使用します。また、`$app/state` や `$app/navigation` などに直接頼るのではなく、現在の URL や navigation action をプロパティとして渡すこともできます。より一般的な方法でアプリを書くことによって、テストや UI デモなどのツールのセットアップも簡単になります。
[エイリアス](configuration#alias) は `svelte.config.js` (`vite.config.js` や `tsconfig.json` ではなく) を経由して追加するようにしてください。`svelte-package` で処理されるからです。.
パッケージに加えた変更がバグフィックスなのか、新機能なのか、それとも破壊的変更(breaking change)なのかをよく考えて、それに応じてパッケージのバージョンを更新する必要があります。もし既存のライブラリから `exports` やその中の `export` condition のパスを削除した場合、breaking change とみなされることにご注意ください。
```json
{
"exports": {
".": {
"types": "./dist/index.d.ts",
// changing `svelte` to `default` is a breaking change:
--- "svelte": "./dist/index.js"---
+++ "default": "./dist/index.js"+++
},
// removing this is a breaking change:
--- "./foo": {
"types": "./dist/foo.d.ts",
"svelte": "./dist/foo.js",
"default": "./dist/foo.js"
},---
// adding this is ok:
+++ "./bar": {
"types": "./dist/bar.d.ts",
"svelte": "./dist/bar.js",
"default": "./dist/bar.js"
}+++
}
}
```
## Source maps
You can create so-called declaration maps (`d.ts.map` files) by setting `"declarationMap": true` in your `tsconfig.json`. This will allow editors such as VS Code to go to the original `.ts` or `.svelte` file when using features like _Go to Definition_. This means you also need to publish your source files alongside your dist folder in a way that the relative path inside the declaration files leads to a file on disk. Assuming that you have all your library code inside `src/lib` as suggested by Svelte's CLI, this is as simple as adding `src/lib` to `files` in your `package.json`:
```json
{
"files": [
"dist",
"!dist/**/*.test.*",
"!dist/**/*.spec.*",
+++"src/lib",
"!src/lib/**/*.test.*",
"!src/lib/**/*.spec.*"+++
]
}
```
## Options
`svelte-package` は以下のオプションを受け付けます:
- `-w`/`--watch` — `src/lib` にあるファイルの変更を関ししてパッケージを再ビルドします
- `-i`/`--input` — パッケージの全てのファイルを含む入力ディレクトリ。デフォルトは `src/lib` です
- `-o`/`--output` — 処理されたファイルが書き込まれる出力ディレクトリ。`package.json` の `exports` はここにあるファイルを指さなければならず、`files` の配列にはこのフォルダを含めなければいけません。デフォルトは `dist` です
- `-p`/`--preserve-output` — パッケージング前に出力ディレクトリの削除を止めるかどうか。デフォルトは `false` で、この場合は出力ディレクトリが最初に空にされます
- `-t`/`--types` — 型定義 (`d.ts` ファイル) を作成するかどうか。エコシステムのライブラリの品質を向上させるため、作成することを強く推奨します。デフォルトは `true` です
- `--tsconfig` - tsconfig または jsconfig へのパス。指定されない場合は、ワークスペースのパスで次の上位の tsconfig/jsconfig を検索します。
## 公開(Publishing)
生成されたパッケージを公開するには:
```sh
npm publish
```
## 注意事項
すべての相対ファイルインポートは、Node の ESM アルゴリズムに従って、フルで指定する必要があります。つまり、`src/lib/something/index.js` のようなファイルには、ファイル名と拡張子を含めなければなりません。
```js
// @errors: 2307
import { something } from './something+++/index.js+++';
```
TypeScript を使用している場合、同じように `.ts` ファイルをインポートする必要がありますが、`.js` ファイルの末尾を使用する必要があります、`.ts` ファイルの末尾ではありません (これは TypeScript の設計上の決定によるもので、私たちの管轄外です)。`tsconfig.json` または `jsconfig.json` に `"moduleResolution": "NodeNext"` を設定すると、これに対処できます。
Svelte ファイル (プロプロセスされる) と TypeScript ファイル (JavaScript にトランスパイルされる) を覗いて、全てのファイルはそのままコピーされます。
# Auth
Auth refers to authentication and authorization, which are common needs when building a web application. Authentication means verifying that the user is who they say they are based on their provided credentials. Authorization means determining which actions they are allowed to take.
## Sessions vs tokens
After the user has provided their credentials such as a username and password, we want to allow them to use the application without needing to provide their credentials again for future requests. Users are commonly authenticated on subsequent requests with either a session identifier or signed token such as a JSON Web Token (JWT).
Session IDs are most commonly stored in a database. They can be immediately revoked, but require a database query to be made on each request.
In contrast, JWT generally are not checked against a datastore, which means they cannot be immediately revoked. The advantage of this method is improved latency and reduced load on your datastore.
## Integration points
Auth [cookies](@sveltejs-kit#Cookies) can be checked inside [server hooks](hooks#Server-hooks). If a user is found matching the provided credentials, the user information can be stored in [`locals`](hooks#Server-hooks-locals).
## Libraries
The [Svelte CLI](/docs/cli) gives the option to [set up Better Auth](https://svelte.dev/docs/cli/better-auth) with a new project or add it to an existing project.
## Guides
If you'd like to implement your own auth system, [the Lucia auth guide](https://lucia-auth.com/) provides a reference for session-based web app auth with SvelteKit examples.
# Performance
Out of the box, SvelteKit does a lot of work to make your applications as performant as possible:
- Code-splitting, so that only the code you need for the current page is loaded
- Asset preloading, so that 'waterfalls' (of files requesting other files) are prevented
- File hashing, so that your assets can be cached forever
- Request coalescing, so that data fetched from separate server `load` functions is grouped into a single HTTP request
- Parallel loading, so that separate universal `load` functions fetch data simultaneously
- Data inlining, so that requests made with `fetch` during server rendering can be replayed in the browser without issuing a new request
- Conservative invalidation, so that `load` functions are only re-run when necessary
- Prerendering (configurable on a per-route basis, if necessary) so that pages without dynamic data can be served instantaneously
- Link preloading, so that data and code requirements for a client-side navigation are eagerly anticipated
Nevertheless, we can't (yet) eliminate all sources of slowness. To eke out maximum performance, you should be mindful of the following tips.
## Diagnosing issues
Google's [PageSpeed Insights](https://pagespeed.web.dev/) and (for more advanced analysis) [WebPageTest](https://www.webpagetest.org/) are excellent ways to understand the performance characteristics of a site that is already deployed to the internet.
Your browser also includes useful developer tools for analysing your site, whether deployed or running locally:
* Chrome - [Lighthouse](https://developer.chrome.com/docs/lighthouse/overview#devtools), [Network](https://developer.chrome.com/docs/devtools/network), and [Performance](https://developer.chrome.com/docs/devtools/performance) devtools
* Edge - [Lighthouse](https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/lighthouse/lighthouse-tool), [Network](https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/network/), and [Performance](https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/evaluate-performance/) devtools
* Firefox - [Network](https://firefox-source-docs.mozilla.org/devtools-user/network_monitor/) and [Performance](https://hacks.mozilla.org/2022/03/performance-tool-in-firefox-devtools-reloaded/) devtools
* Safari - [enhancing the performance of your webpage](https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/Web_Inspector_Tutorial/EnhancingyourWebpagesPerformance/EnhancingyourWebpagesPerformance.html)
Note that your site running locally in `dev` mode will exhibit different behaviour than your production app, so you should do performance testing in [preview](building-your-app#Preview-your-app) mode after building.
### Instrumenting
If you see in the network tab of your browser that an API call is taking a long time and you'd like to understand why, you may consider instrumenting your backend with a tool like [OpenTelemetry](https://opentelemetry.io/) or [Server-Timing headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing).
## Optimizing assets
### Images
Reducing the size of image files is often one of the most impactful changes you can make to a site's performance. Svelte provides the `@sveltejs/enhanced-img` package, detailed on the [images](images) page, for making this easier. Additionally, Lighthouse is useful for identifying the worst offenders.
### Videos
Video files can be very large, so extra care should be taken to ensure that they're optimized:
- Compress videos with tools such as [Handbrake](https://handbrake.fr/). Consider converting the videos to web-friendly formats such as `.webm` or `.mp4`.
- You can [lazy-load videos](https://web.dev/articles/lazy-loading-video) located below the fold with `preload="none"` (though note that this will slow down playback when the user _does_ initiate it).
- Strip the audio track out of muted videos using a tool like [FFmpeg](https://ffmpeg.org/).
### Fonts
SvelteKit automatically preloads critical `.js` and `.css` files when the user visits a page, but it does _not_ preload fonts by default, since this may cause unnecessary files (such as font weights that are referenced by your CSS but not actually used on the current page) to be downloaded. Having said that, preloading fonts correctly can make a big difference to how fast your site feels. In your [`handle`](hooks#Server-hooks-handle) hook, you can call `resolve` with a `preload` filter that includes your fonts.
You can reduce the size of font files by [subsetting](https://web.dev/learn/performance/optimize-web-fonts#subset_your_web_fonts) your fonts.
## Reducing code size
### Svelte version
We recommend running the latest version of Svelte. Svelte 5 is smaller and faster than Svelte 4, which is smaller and faster than Svelte 3.
### Packages
[`rollup-plugin-visualizer`](https://www.npmjs.com/package/rollup-plugin-visualizer) can be helpful for identifying which packages are contributing the most to the size of your site. You may also find opportunities to remove code by manually inspecting the build output (use `build: { minify: false }` in your [Vite config](https://vitejs.dev/config/build-options.html#build-minify) to make the output readable, but remember to undo that before deploying your app), or via the network tab of your browser's devtools.
### External scripts
Try to minimize the number of third-party scripts running in the browser. For example, instead of using JavaScript-based analytics consider using server-side implementations, such as those offered by many platforms with SvelteKit adapters including [Cloudflare](https://www.cloudflare.com/web-analytics/), [Netlify](https://docs.netlify.com/monitor-sites/site-analytics/), and [Vercel](https://vercel.com/docs/analytics).
To run third party scripts in a web worker (which avoids blocking the main thread), use [Partytown's SvelteKit integration](https://partytown.builder.io/sveltekit).
### Selective loading
Code imported with static `import` declarations will be automatically bundled with the rest of your page. If there is a piece of code you need only when some condition is met, use the dynamic `import(...)` form to selectively lazy-load the component.
## Navigation
### Preloading
You can speed up client-side navigations by eagerly preloading the necessary code and data, using [link options](link-options). This is configured by default on the `` element when you create a new SvelteKit app.
### Non-essential data
For slow-loading data that isn't needed immediately, the object returned from your `load` function can contain promises rather than the data itself. For server `load` functions, this will cause the data to [stream](load#Streaming-with-promises) in after the navigation (or initial page load).
### Preventing waterfalls
One of the biggest performance killers is what is referred to as a _waterfall_, which is a series of requests that is made sequentially. This can happen on the server or in the browser, but is especially costly when dealing with data that has to travel further or across slower networks, such as a mobile user making a call to a distant server.
In the browser, waterfalls can occur when your HTML kicks off request chains such as requesting JS which requests CSS which requests a background image and web font. SvelteKit will largely solve this class of problems for you by adding [`modulepreload`](https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/modulepreload) tags or headers, but you should view [the network tab in your devtools](#Diagnosing-issues) to check whether additional resources need to be preloaded.
- Pay special attention to this if you use [web fonts](#Optimizing-assets-Fonts) since they need to be handled manually.
- Enabling [single page app (SPA) mode](single-page-apps) will cause such waterfalls. With SPA mode, an empty page is generated, which fetches JavaScript, which ultimately loads and renders the page. This results in extra network round trips before a single pixel can be displayed.
Waterfalls can also occur on calls to the backend whether made from the browser or server. E.g. if a universal `load` function makes an API call to fetch the current user, then uses the details from that response to fetch a list of saved items, and then uses _that_ response to fetch the details for each item, the browser will end up making multiple sequential requests. This is deadly for performance, especially for users that are physically located far from your backend.
- Avoid this issue by using [server `load` functions](load#Universal-vs-server) to make requests to backend services that are dependencies from the server rather than from the browser. Note, however, that server `load` functions are also not immune to waterfalls (though they are much less costly since they rarely involve round trips with high latency). For example, if you query a database to get the current user and then use that data to make a second query for a list of saved items, it will typically be more performant to issue a single query with a database join.
## Hosting
Your frontend should be located in the same data center as your backend to minimize latency. For sites with no central backend, many SvelteKit adapters support deploying to the _edge_, which means handling each user's requests from a nearby server. This can reduce load times significantly. Some adapters even support [configuring deployment on a per-route basis](page-options#config). You should also consider serving images from a CDN (which are typically edge networks) — the hosts for many SvelteKit adapters will do this automatically.
Ensure your host uses HTTP/2 or newer. Vite's code splitting creates numerous small files for improved cacheability, which results in excellent performance, but this does assume that your files can be loaded in parallel with HTTP/2.
## Further reading
For the most part, building a performant SvelteKit app is the same as building any performant web app. You should be able to apply information from general performance resources such as [Core Web Vitals](https://web.dev/explore/learn-core-web-vitals) to any web experience you build.
# Icons
## CSS
アイコンの利用において、優れた手法のひとつが CSS を用いて定義する方法です。Iconifyは [多くの人気アイコンセット](https://icon-sets.iconify.design/) をサポートしており、[CSSで組み込むことができます](https://iconify.design/docs/usage/css/)。この方法は、Iconifyの [Tailwind CSS プラグイン](https://iconify.design/docs/usage/css/tailwind/) や [UnoCSS プラグイン](https://iconify.design/docs/usage/css/unocss/) を活用することで、人気のCSSフレームワークと組み合わせて使うことも可能です。Svelteコンポーネントベースのライブラリとは異なり、各アイコンを `.svelte` ファイルにインポートする必要がありません。
## Svelte
[Svelte用のアイコンライブラリ](/packages#icons) は数多くあります。アイコンライブラリを選択する際は、アイコンごとに `.svelte` ファイルを提供するものは避けることをお勧めします。これらのライブラリは数千の `.svelte` ファイルを持つ可能性があり、[Viteの依存関係最適化](https://vite.dev/guide/dep-pre-bundling.html) を大幅に遅くしてしまいます。これは [`vite-plugin-svelte`のFAQで説明されている](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/faq.md#what-is-going-on-with-vite-and-pre-bundling-dependencies) ように、アイコンを umbrella import と subpath import の両方で読み込んでしまうことで、パフォーマンスの問題が顕著になる可能性があるためです。
# Images
Images can have a big impact on your app's performance. For best results, you should optimize them by doing the following:
- generate optimal formats like `.avif` and `.webp`
- create different sizes for different screens
- ensure that assets can be cached effectively
Doing this manually is tedious. There are a variety of techniques you can use, depending on your needs and preferences.
## Vite's built-in handling
[Vite will automatically process imported assets](https://vitejs.dev/guide/assets.html) for improved performance. This includes assets referenced via the CSS `url()` function. Hashes will be added to the filenames so that they can be cached, and assets smaller than `assetsInlineLimit` will be inlined. Vite's asset handling is most often used for images, but is also useful for video, audio, etc.
```svelte
` rather than `` tag will be replaced with an `` providing multiple image types and sizes. It's only possible to downscale images without losing quality, which means that you should provide the highest resolution image that you need — smaller versions will be generated for the various device types that may request an image.
You should provide your image at 2x resolution for HiDPI displays (a.k.a. retina displays). `` will automatically take care of serving smaller versions to smaller devices.
> [!NOTE] if you wish to use a [tag name CSS selector](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Styling_basics/Basic_selectors#type_selectors) in your `
```
### `srcset` and `sizes`
If you have a large image, such as a hero image taking the width of the design, you should specify `sizes` so that smaller versions are requested on smaller devices. E.g. if you have a 1280px image you may want to specify something like:
```svelte
` will generate small images for smaller devices and populate the `srcset` attribute.
The smallest picture generated automatically will have a width of 540px. If you'd like smaller images or would otherwise like to specify custom widths, you can do that with the `w` query parameter:
```svelte
` tags with multiple sources. Finally, some CDNs may generate images lazily, which could have a negative performance impact for sites with low traffic and frequently changing images.
CDNs can generally be used without any need for a library. However, there are a number of libraries with Svelte support that make it easier. [`@unpic/svelte`](https://unpic.pics/img/svelte/) is a CDN-agnostic library with support for a large number of providers. You may also find that specific CDNs like [Cloudinary](https://svelte.cloudinary.dev/) have Svelte support. Finally, some content management systems (CMS) which support Svelte (such as [Contentful](https://www.contentful.com/sveltekit-starter-guide/), [Storyblok](https://www.storyblok.com/docs/guides/svelte), and [Contentstack](https://www.contentstack.com/docs/developers/sample-apps/build-a-starter-website-with-sveltekit-and-contentstack)) have built-in support for image handling.
## Best practices
- For each image type, use the appropriate solution from those discussed above. You can mix and match all three solutions in one project. For example, you may use Vite's built-in handling to provide images for `` タグをクリックするなど) で、ページのフルリロードを引き起こします。これが起こると、スクリーンリーダーやその他の支援技術が新しいページのタイトルを読み上げ、それによってユーザーはページが変更されたことを理解します。
SvelteKit では、ページ間のナビゲーションではページのリロードが発生しないため ([クライアントサイドルーティング](glossary#Routing)として知られる)、SvelteKit はナビゲーションごとに新しいページ名が読み上げられるように[ライブリージョン](https://developer.mozilla.org/ja/docs/Web/Accessibility/ARIA/ARIA_Live_Regions)をページに注入します。これは、`` 要素を検査することで、アナウンスするページ名を決定します。
この動作のために、アプリの全ページにユニークで説明的なタイトルを付けるべきです。SvelteKit では、各ページに `<svelte:head>` 要素を配置することでこれを行うことができます:
```svelte
<!--- file: src/routes/+page.svelte --->
<svelte:head>
<title>Todo List
```
これにより、スクリーンリーダーやその他の支援技術が、ナビゲーション後に新しいページを識別することができるようになります。説明的なタイトルを提供することは、[SEO](seo#Manual-setup-title-and-meta) にとっても重要なことです。
## フォーカス管理
旧来のサーバーレンダリングアプリケーションでは、ナビゲーションでフォーカスがページのトップにリセットされます。これによって、キーボードやスクリーンリーダーを使用して web をブラウジングする方が、ページの先頭からやり取りできるようになります。
クライアントサイドルーティング中にこの挙動をシミュレートするために、SvelteKit は各ナビゲーションや [強化されたフォーム送信(enhanced form submission)](https://kit.svelte.jp/docs/form-actions#Progressive-enhancement) の後、`` 要素にフォーカスを合わせます。1つ例外があります - [`autofocus`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/autofocus) 属性が付いている要素が存在する場合、SvelteKit はその要素にフォーカスを合わせます。この属性を使用するときは、[支援技術(assistive technology)に対する影響を必ず考慮](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/autofocus#accessibility_considerations)してください。
SvelteKit のフォーカス管理をカスタマイズしたい場合は、`afterNavigate` hook を使います:
```js
/// ` と `<meta name="description">` を [`<svelte:head>`](../svelte/svelte-head) の内側に置くべきです。説明的な title と description の書き方に関するガイダンスと、検索エンジンにとってわかりやすいコンテンツを作るためのその他の方法については、Google の [Lighthouse SEO audits](https://web.dev/lighthouse-seo/) のドキュメントで見つけることができます。
> [!NOTE] よくあるパターンとしては、ページの [`load`](load) 関数から SEO 関連の `data` を返し、それを最上位の[レイアウト](routing#layout)の `<svelte:head>` で ([`page.data`]($app-state) として) 使用することです。
### サイトマップ <!--Sitemaps-->
[サイトマップ](https://developers.google.com/search/docs/advanced/sitemaps/build-sitemap) は、検索エンジンがサイト内のページの優先順位付けをするのに役立ちます、特にコンテンツの量が多い場合は。エンドポイントを使用してサイトマップを動的に作成できます:
```js
/// file: src/routes/sitemap.xml/+server.js
export async function GET() {
return new Response(
`
<?xml version="1.0" encoding="UTF-8" ?>
<urlset
xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:mobile="http://www.google.com/schemas/sitemap-mobile/1.0"
xmlns:news="http://www.google.com/schemas/sitemap-news/0.9"
xmlns:image="http://www.google.com/schemas/sitemap-image/1.1"
xmlns:video="http://www.google.com/schemas/sitemap-video/1.1"
>
<!-- <url> elements go here -->
</urlset>`.trim(),
{
headers: {
'Content-Type': 'application/xml'
}
}
);
}
```
### AMP
現代の web 開発における不幸な現実として、サイトの [Accelerated Mobile Pages (AMP)](https://amp.dev/) バージョンを作らなければならないときがある、というのがあります。SvelteKit では、[`inlineStyleThreshold`](configuration#inlineStyleThreshold) オプションを設定することでこれを実現することができます…
```js
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
// since <link rel="stylesheet"> isn't
// allowed, inline all styles
inlineStyleThreshold: Infinity
}
};
export default config;
```
…最上位(root)の `+layout.js`/`+layout.server.js` の `csr` を無効にします…
```js
/// file: src/routes/+layout.server.js
export const csr = false;
```
…`amp` を `app.html` に追加します
```html
<html amp>
...
```
…そして、`transformPageChunk` と、`@sveltejs/amp` からインポートできる `transform` を使用して、HTML を変換します:
```js
/// file: src/hooks.server.js
import * as amp from '@sveltejs/amp';
/** @type {import('@sveltejs/kit').Handle} */
export async function handle({ event, resolve }) {
let buffer = '';
return await resolve(event, {
transformPageChunk: ({ html, done }) => {
buffer += html;
if (done) return amp.transform(buffer);
}
});
}
```
ページを amp に変換した結果として未使用の CSS が配布されてしまうのを防ぎたければ、[`dropcss`](https://www.npmjs.com/package/dropcss) を使用すると良いでしょう:
```js
// @filename: ambient.d.ts
declare module 'dropcss';
// @filename: index.js
// ---cut---
/// file: src/hooks.server.js
// @errors: 2307
import * as amp from '@sveltejs/amp';
import dropcss from 'dropcss';
/** @type {import('@sveltejs/kit').Handle} */
export async function handle({ event, resolve }) {
let buffer = '';
return await resolve(event, {
transformPageChunk: ({ html, done }) => {
buffer += html;
if (done) {
let css = '';
const markup = amp
.transform(buffer)
.replace('⚡', 'amp') // dropcss can't handle this character
.replace(/<style amp-custom([^>]*?)>([^]+?)<\/style>/, (match, attributes, contents) => {
css = contents;
return `<style amp-custom${attributes}></style>`;
});
css = dropcss({ css, html: markup }).css;
return markup.replace('</style>', `${css}</style>`);
}
}
});
}
```
> [!NOTE] `amphtml-validator` を使用して変換された HTML を検証するのに、`handle` hook を利用するのは良いアイデアですが、非常に遅くなってしまうので、ページをプリレンダリングするときだけにしてください。
# Frequently asked questions
## Other resources
[Svelte FAQ](../svelte/faq) と [`vite-plugin-svelte` FAQ](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/faq.md) も、これらのライブラリに起因する疑問点には役立ちますのでご参照ください。
## What can I make with SvelteKit?
See [the documentation regarding project types](project-types) for more details.
## package.json の詳細をアプリケーションに含めるにはどうすればよいですか？ <!--How-do-I-include-details-from-package.json-in-my-application-->
アプリケーションで、アプリケーションのバージョン番号やその他の情報を `package.json` から読み込みたい場合は、このように JSON を読み込むことができます:
```ts
// @errors: 2732
/// file: svelte.config.js
import pkg from './package.json' with { type: 'json' };
```
## パッケージをインクルードしようとするとエラーが発生するのですが、どうすれば直せますか？ <!--How-do-I-fix-the-error-I-m-getting-trying-to-include-a-package-->
ライブラリのインクルードに関する問題は、ほとんどが不適切なパッケージングによるものです。ライブラリのパッケージングが Node.js に対応しているかどうかは、[publint の web サイト](https://publint.dev/) でチェックできます。
以下は、ライブラリが正しくパッケージングされているかどうかをチェックする際に気を付けるべき点です:
- `exports` は `main` や `module` などの他のエントリーポイントのフィールドよりも優先されます。`exports` フィールドを追加すると、deep import を妨げることになるため、後方互換性が失われる場合があります。
- `"type": "module"` が指定されていない限り、ESM ファイルは `.mjs` で終わる必要があり、CommonJS ファイルは `.cjs` で終わる必要があります。
- `exports` が定義されていない場合、`main` を定義する必要があり、それは CommonJS ファイル か ESM ファイル でなければならず、前項に従わなければなりません。`module` フィールドが定義されている場合、ESM ファイルを参照している必要があります。
- Svelte コンポーネントは、コンパイルされていない `.svelte` ファイルとして配布し、パッケージに含まれる JS は ESM のみとして記述していなければなりません。TypeScript などのカスタムスクリプトや SCSS などのスタイル言語は、それぞれ vanilla JS と CSS にするために前処理(preprocess)をしなければなりません。Svelte ライブラリのパッケージングには、[`svelte-package`](./packaging) を使用することを推奨しています。このパッケージによって、これらの作業が行われます。
ライブラリが ESM バージョンを配布している場合、特に Svelte コンポーネントライブラリがその依存関係に含まれている場合、Vite を使用するとブラウザ上で最適に動作します。ライブラリの作者に ESM バージョンを提供するよう提案すると良いでしょう。しかし、CommonJS (CJS) の依存関係も上手く扱えるようにするため、デフォルトで、[`vite-plugin-svelte` が Vite にそれらを事前バンドルするよう指示します](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/faq.md#what-is-going-on-with-vite-and-pre-bundling-dependencies)。Vite は `esbuild` を使ってそれらを ESM に変換します。
それでもまだ問題が解消されない場合は、[Vite の issue tracker](https://github.com/vitejs/vite/issues) と 該当のライブラリの issue tracker を検索することを推奨します。[`optimizeDeps`](https://vitejs.dev/config/#dep-optimization-options) や [`ssr`](https://vitejs.dev/config/#ssr-options) の設定値をいじることで問題を回避できる場合もありますが、これはあくまで一時的な回避策とし、問題のあるライブラリの修正を優先したほうが良いでしょう。
## view transitions API を使うにはどうすればよいですか？ <!--How-do-I-use-the-view-transitions-API-->
SvelteKit では [view transitions](https://developer.chrome.com/docs/web-platform/view-transitions/) 向けの特別なインテグレーションはありませんが、[`onNavigate`]($app-navigation#onNavigate) の中で `document.startViewTransition` を呼び出すことにより、クライアントサイドナビゲーション毎に view transition をトリガーすることができます。
```js
// @errors: 2339 2810
import { onNavigate } from '$app/navigation';
onNavigate((navigation) => {
if (!document.startViewTransition) return;
return new Promise((resolve) => {
document.startViewTransition(async () => {
resolve();
await navigation.complete;
});
});
});
```
もっと詳しく知りたければ、Svelte ブログの ["Unlocking view transitions"](/blog/view-transitions) をご参照ください。
## データベースのセットアップはどう行えばよいですか？ <!--How-do-I-set-up-a-database-->
データベースにクエリするコードを [サーバールート(server route)](./routing#server) に置いてください。.svelte ファイルの中でデータベースにクエリしないでください。コネクションをすぐにセットアップし、シングルトンとしてアプリ全体からクライアントにアクセスできるように `db.js` のようなものを作ると良いでしょう。`hooks.server.js` で1回セットアップするコードを実行し、データベースヘルパーを必要とするすべてのエンドポイントにインポートできます。
You can use [the Svelte CLI](/docs/cli/overview) to automatically set up database integrations.
## `document` や `window` にアクセスするクライアントサイドライブラリはどう使えばよいですか？ <!--How-do-I-use-a-client-side-library-accessing-document-or-window-->
もし `document` や `window` 変数にアクセスする必要があったり、クライアントサイドだけで実行するコードが必要な場合は、`browser` チェックでラップしてください:
```js
/// <reference types="@sveltejs/kit" />
// ---cut---
import { browser } from '$app/environment';
if (browser) {
// client-only code here
}
```
コンポーネントが最初に DOM にレンダリングされた後にコードを実行したい場合は、`onMount` で実行することもできます:
```js
// @filename: ambient.d.ts
// @lib: ES2015
declare module 'some-browser-only-library';
// @filename: index.js
// ---cut---
import { onMount } from 'svelte';
onMount(async () => {
const { method } = await import('some-browser-only-library');
method('hello world');
});
```
使用したいライブラリに副作用がなければ静的にインポートすることができますし、サーバー側のビルドでツリーシェイクされ、`onMount` が自動的に no-op に置き換えられます:
```js
// @filename: ambient.d.ts
// @lib: ES2015
declare module 'some-browser-only-library';
// @filename: index.js
// ---cut---
import { onMount } from 'svelte';
import { method } from 'some-browser-only-library';
onMount(() => {
method('hello world');
});
```
最後に、`{#await}` ブロックのご使用も検討してみてください:
```svelte
<!--- file: index.svelte --->
<script>
import { browser } from '$app/environment';
const ComponentConstructor = browser ?
import('some-browser-only-library').then((module) => module.Component) :
new Promise(() => {});
</script>
{#await ComponentConstructor}
<p>Loading...</p>
{:then component}
<svelte:component this={component} />
{:catch error}
<p>Something went wrong: {error.message}</p>
{/await}
```
## 別のバックエンド API サーバーを使用するにはどうすれば良いですか？ <!--How-do-I-use-a-different-backend-API-server-->
外部の API サーバーにデータをリクエストするのに [`event.fetch`](./load#Making-fetch-requests) を使用することができますが、[CORS](https://developer.mozilla.org/ja/docs/Web/HTTP/CORS) に対応しなければならず、一般的にはリクエストのプリフライトが必要になり、結果として高レイテンシーになるなど、複雑になることにご注意ください。別のサブドメインへのリクエストも、追加の DNS ルックアップや TLS セットアップなどのためにレイテンシーが増加する可能性があります。この方法を使いたい場合は、[`handleFetch`](./hooks#Server-hooks-handleFetch) が参考になるかもしれません。
別の方法は、頭痛の種である CORS をバイパスするためのプロキシーをセットアップすることです。本番環境では、`/api` などのパスを API サーバーに書き換えます(rewrite)。ローカルの開発環境では、Vite の [`server.proxy`](https://vitejs.dev/config/server-options.html#server-proxy) オプションを使用します。
本番環境で書き換え(rewrite)をセットアップする方法は、デプロイ先のプラットフォームに依存します。もし、書き換える方法がなければ、代わりに [API route](./routing#server) を追加します:
```js
/// file: src/routes/api/[...path]/+server.js
/** @type {import('./$types').RequestHandler} */
export function GET({ params, url }) {
return fetch(`https://example.com/${params.path + url.search}`);
}
```
(必要に応じて、`POST`/`PATCH` などのリクエストもプロキシし、`request.headers` も転送(forward)する必要があることにご注意ください)
## ミドルウェア(middleware)を使うにはどうすればよいですか？ <!--How-do-I-use-middleware-->
`adapter-node` は、プロダクションモードで使用するためのミドルウェアを自分のサーバで構築します。開発モードでは、Vite プラグインを使用して Vite にミドルウェア(middleware) を追加することができます。例えば:
```js
/// file: vite.config.js
import { sveltekit } from '@sveltejs/kit/vite';
/** @type {import('vite').Plugin} */
const myPlugin = {
name: 'log-request-middleware',
configureServer(server) {
server.middlewares.use((req, res, next) => {
console.log(`Got request ${req.url}`);
next();
});
}
};
/** @type {import('vite').UserConfig} */
const config = {
plugins: [myPlugin, sveltekit()]
};
export default config;
```
順序を制御する方法など、詳しくは [Vite の `configureServer` のドキュメント](https://vitejs.dev/guide/api-plugin.html#configureserver) をご覧ください。
## Yarn を使うには？ <!--How-do-I-use-Yarn-->
### Yarn 2 で動作しますか？ <!--Does-it-work-with-Yarn-2-->
Sort of. The Plug'n'Play feature, aka 'pnp', is broken (it deviates from the Node module resolution algorithm, and [doesn't yet work with native JavaScript modules](https://github.com/yarnpkg/berry/issues/638) which SvelteKit — along with an [increasing number of packages](https://github.com/wooorm/npm-esm-vs-cjs) — uses). You can use `nodeLinker: 'node-modules'` in your [`.yarnrc.yml`](https://yarnpkg.com/configuration/yarnrc#nodeLinker) file to disable pnp, but it's probably easier to just use npm or [pnpm](https://pnpm.io/), which is similarly fast and efficient but without the compatibility headaches.
### Yarn 3 を使用するにはどうすれば良いですか？ <!--How-do-I-use-with-Yarn-3-->
現時点の、最新の Yarn (version 3) の ESM サポート は [experimental](https://github.com/yarnpkg/berry/pull/2161) であるようです。
結果は異なるかもしれませんが、下記が有効なようです。最初に新しいアプリケーションを作成します:
```sh
yarn create svelte myapp
cd myapp
```
And enable Yarn Berry:
```sh
yarn set version berry
yarn install
```
Yarn Berry の興味深い機能の1つに、ディスク上のプロジェクトごとに複数のコピーを持つのではなく、パッケージ用に単一のグローバルキャッシュを持つことができる、というのがあります。しかし、`enableGlobalCache` の設定を true にするとビルドが失敗するため、`.yarnrc.yml` ファイルに以下を追加することを推奨します:
```yaml
nodeLinker: node-modules
```
これによってパッケージはローカルの node_modules ディレクトリにダウンロードされますが、上記の問題は回避され、現時点では Yarn の version 3 を使用するベストな方法となります。
# Integrations
## `vitePreprocess`
[`vitePreprocess`](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/preprocess.md) preprocesses `<style>` and `<script>` tags in `.svelte` files.
```js
// svelte.config.js
import { vitePreprocess } from '@sveltejs/vite-plugin-svelte';
/** @type {import('@sveltejs/kit').Config} */
const config = {
preprocess: [
vitePreprocess({
style: true, // default value
script: false // default value
})
]
};
export default config;
```
### `style`
Use `vitePreprocess()` to enable CSS preprocessors in `<style>` tags: PostCSS, SCSS, Less, Stylus, and SugarSS.
### `script`
Use `vitePreprocess({ script: true })` if:
- your project is before Svelte 5
- you are using advanced TypeScript features that emit code _(check [`vitePreprocess`](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/preprocess.md) documentation)_
> [!NOTE]
TypeScript is supported natively in Svelte 5, so if you are using Svelte 5 and you don't need to use advanced TypeScript features that emit code, you probably don't need to use `vitePreprocess`.
## Add-ons
[`npx sv add`](/docs/cli/sv-add) を実行することで、様々な複雑なインテグレーションを単一のコマンドでセットアップすることができます:
- prettier (formatting)
- eslint (linting)
- vitest (unit testing)
- playwright (e2e testing)
- better-auth (auth)
- tailwind (CSS)
- drizzle (DB)
- paraglide (i18n)
- mdsvex (markdown)
- storybook (frontend workshop)
- adapters (hosting)
- mcp (LLM tooling)
## Packages
厳選された高品質な Svelte パッケージの一覧については [パッケージページ](/packages) をご覧ください。また、追加のライブラリ、テンプレート、リソースについては [sveltesociety.dev](https://sveltesociety.dev/) をご覧ください。
## Additional integrations
### `svelte-preprocess`
`svelte-preprocess` は、Pug、Babel、global styles のサポートなど、`vitePreprocess` には無い機能があります。しかし、`vitePreprocess` はより速く、設定が少ないため、デフォルトでは `vitePreprocess` が使用されます。SvelteKit は CoffeeScript を [サポートしていない](https://github.com/sveltejs/kit/issues/2920#issuecomment-996469815) ことにご注意ください。
`svelte-preprocess` をインストールするには `npm i -D svelte-preprocess` を実行し、ご自身で [`svelte.config.js` に追加する](https://github.com/sveltejs/svelte-preprocess/blob/main/docs/usage.md#with-svelte-config) 必要があります。その後、`npm i -D sass` や `npm i -D less` など、[対応するライブラリのインストール](https://github.com/sveltejs/svelte-preprocess/blob/main/docs/getting-started.md) が必要になることが多いようです。
## Vite plugins
SvelteKit プロジェクトは Vite で構築されているため、Vite plugin を使用してプロジェクトを拡張することができます。利用可能な plugin のリストは [`vitejs/awesome-vite`](https://github.com/vitejs/awesome-vite?tab=readme-ov-file#plugins) をご覧ください。
## Integration FAQs
[SvelteKit FAQ](./faq) にて、SvelteKit で X をする方法に関する多くの質問に対する回答があるので、、もしまだ不明点があるようでしたら役に立つかもしれません。
# Breakpoint Debugging
In addition to the [`@debug`](../svelte/@debug) tag, you can also debug Svelte and SvelteKit projects using breakpoints within various tools and development environments. This includes both frontend and backend code.
The following guides assume your JavaScript runtime environment is Node.js.
## Visual Studio Code
With the built-in debug terminal, you can set up breakpoints in source files within VSCode.
1. Open the command palette: `CMD/Ctrl` + `Shift` + `P`.
2. Find and launch "Debug: JavaScript Debug Terminal".
3. Start your project using the debug terminal. For example: `npm run dev`.
4. Set some breakpoints in your client or server-side source code.
5. Trigger the breakpoint.
### Launch via debug pane
You may alternatively set up a `.vscode/launch.json` in your project. To set one up automatically:
1. Go to the "Run and Debug" pane.
2. In the "Run" select menu, choose "Node.js...".
3. Select the "run script" that corresponds to your project, such as "Run script: dev".
4. Press the "Start debugging" play button, or hit `F5` to begin breakpoint debugging.
Here's an example `launch.json`:
```json
{
"version": "0.2.0",
"configurations": [
{
"command": "npm run dev",
"name": "Run development server",
"request": "launch",
"type": "node-terminal"
}
]
}
```
Further reading: <https://code.visualstudio.com/docs/editor/debugging>.
## Other Editors
If you use a different editor, these community guides might be useful for you:
- [WebStorm Svelte: Debug Your Application](https://www.jetbrains.com/help/webstorm/svelte.html#ws_svelte_debug)
- [Debugging JavaScript Frameworks in Neovim](https://theosteiner.de/debugging-javascript-frameworks-in-neovim)
## Google Chrome and Microsoft Edge Developer Tools
It's possible to debug Node.js applications using a browser-based debugger.
> [!NOTE] Note this only works with debugging client-side SvelteKit source maps.
1. Run the `--inspect` flag when starting the Vite server with Node.js. For instance: `NODE_OPTIONS="--inspect" npm run dev`
2. Open your site in a new tab. Typically at `localhost:5173`.
3. Open your browser's dev tools, and click on the "Open dedicated DevTools for Node.js" icon near the top-left. It should display the Node.js logo.
4. Set up breakpoints and debug your application.
You may alternatively open the debugger devtools by navigating to `chrome://inspect` in Google Chrome, or `edge://inspect` in Microsoft Edge.
## References
- [Debugging Node.js](https://nodejs.org/en/learn/getting-started/debugging)
# Migrating to SvelteKit v2
Upgrading from SvelteKit version 1 to version 2 should be mostly seamless. There are a few breaking changes to note, which are listed here. You can use `npx sv migrate sveltekit-2` to migrate some of these changes automatically.
We highly recommend upgrading to the most recent 1.x version before upgrading to 2.0, so that you can take advantage of targeted deprecation warnings. We also recommend [updating to Svelte 4](../svelte/v4-migration-guide) first: Later versions of SvelteKit 1.x support it, and SvelteKit 2.0 requires it.
## `redirect` and `error` are no longer thrown by you
Previously, you had to `throw` the values returned from `error(...)` and `redirect(...)` yourself. In SvelteKit 2 this is no longer the case — calling the functions is sufficient.
```js
import { error } from '@sveltejs/kit'
// ...
---throw error(500, 'something went wrong');---
+++error(500, 'something went wrong');+++
```
`svelte-migrate` will do these changes automatically for you.
If the error or redirect is thrown inside a `try {...}` block (hint: don't do this!), you can distinguish them from unexpected errors using [`isHttpError`](@sveltejs-kit#isHttpError) and [`isRedirect`](@sveltejs-kit#isRedirect) imported from `@sveltejs/kit`.
## path is required when setting cookies
When receiving a `Set-Cookie` header that doesn't specify a `path`, browsers will [set the cookie path](https://www.rfc-editor.org/rfc/rfc6265#section-5.1.4) to the parent of the resource in question. This behaviour isn't particularly helpful or intuitive, and frequently results in bugs because the developer expected the cookie to apply to the domain as a whole.
As of SvelteKit 2.0, you need to set a `path` when calling `cookies.set(...)`, `cookies.delete(...)` or `cookies.serialize(...)` so that there's no ambiguity. Most of the time, you probably want to use `path: '/'`, but you can set it to whatever you like, including relative paths — `''` means 'the current path', `'.'` means 'the current directory'.
```js
/** @type {import('./$types').PageServerLoad} */
export function load({ cookies }) {
cookies.set(name, value, +++{ path: '/' }+++);
return { response }
}
```
`svelte-migrate` will add comments highlighting the locations that need to be adjusted.
## Top-level promises are no longer awaited
In SvelteKit version 1, if the top-level properties of the object returned from a `load` function were promises, they were automatically awaited. With the introduction of [streaming](/blog/streaming-snapshots-sveltekit) this behavior became a bit awkward as it forces you to nest your streamed data one level deep.
As of version 2, SvelteKit no longer differentiates between top-level and non-top-level promises. To get back the blocking behavior, use `await` (with `Promise.all` to prevent waterfalls, where appropriate):
```js
// @filename: ambient.d.ts
declare const url: string;
// @filename: index.js
// ---cut---
// If you have a single promise
/** @type {import('./$types').PageServerLoad} */
export +++async+++ function load({ fetch }) {
const response = +++await+++ fetch(url).then(r => r.json());
return { response }
}
```
```js
// @filename: ambient.d.ts
declare const url1: string;
declare const url2: string;
// @filename: index.js
// ---cut---
// If you have multiple promises
/** @type {import('./$types').PageServerLoad} */
export +++async+++ function load({ fetch }) {
--- const a = fetch(url1).then(r => r.json());---
--- const b = fetch(url2).then(r => r.json());---
+++ const [a, b] = await Promise.all([
fetch(url1).then(r => r.json()),
fetch(url2).then(r => r.json()),
]);+++
return { a, b };
}
```
## goto(...) changes
`goto(...)` no longer accepts external URLs. To navigate to an external URL, use `window.location.href = url`. The `state` object now determines `$page.state` and must adhere to the `App.PageState` interface, if declared. See [shallow routing](shallow-routing) for more details.
## paths are now relative by default
In SvelteKit 1, `%sveltekit.assets%` in your `app.html` was replaced with a relative path by default (i.e. `.` or `..` or `../..` etc, depending on the path being rendered) during server-side rendering unless the [`paths.relative`](configuration#paths) config option was explicitly set to `false`. The same was true for `base` and `assets` imported from `$app/paths`, but only if the `paths.relative` option was explicitly set to `true`.
This inconsistency is fixed in version 2. Paths are either always relative or always absolute, depending on the value of [`paths.relative`](configuration#paths). It defaults to `true` as this results in more portable apps: if the `base` is something other than the app expected (as is the case when viewed on the [Internet Archive](https://archive.org/), for example) or unknown at build time (as is the case when deploying to [IPFS](https://ipfs.tech/) and so on), fewer things are likely to break.
## Server fetches are not trackable anymore
Previously it was possible to track URLs from `fetch`es on the server in order to rerun load functions. This poses a possible security risk (private URLs leaking), and for this reason it was behind the `dangerZone.trackServerFetches` setting, which is now removed.
## `preloadCode` arguments must be prefixed with `base`
SvelteKit exposes two functions, [`preloadCode`]($app-navigation#preloadCode) and [`preloadData`]($app-navigation#preloadData), for programmatically loading the code and data associated with a particular path. In version 1, there was a subtle inconsistency — the path passed to `preloadCode` did not need to be prefixed with the `base` path (if set), while the path passed to `preloadData` did.
This is fixed in SvelteKit 2 — in both cases, the path should be prefixed with `base` if it is set.
Additionally, `preloadCode` now takes a single argument rather than _n_ arguments.
## `resolvePath` has been removed
SvelteKit 1 included a function called `resolvePath` which allows you to resolve a route ID (like `/blog/[slug]`) and a set of parameters (like `{ slug: 'hello' }`) to a pathname. Unfortunately the return value didn't include the `base` path, limiting its usefulness in cases where `base` was set.
For this reason, SvelteKit 2 replaces `resolvePath` with a (slightly better named) function called `resolveRoute`, which is imported from `$app/paths` and which takes `base` into account.
```js
---import { resolvePath } from '@sveltejs/kit';
import { base } from '$app/paths';---
+++import { resolveRoute } from '$app/paths';+++
---const path = base + resolvePath('/blog/[slug]', { slug });---
+++const path = resolveRoute('/blog/[slug]', { slug });+++
```
`svelte-migrate` will do the method replacement for you, though if you later prepend the result with `base`, you need to remove that yourself.
## Improved error handling
Errors are handled inconsistently in SvelteKit 1. Some errors trigger the `handleError` hook but there is no good way to discern their status (for example, the only way to tell a 404 from a 500 is by seeing if `event.route.id` is `null`), while others (such as 405 errors for `POST` requests to pages without actions) don't trigger `handleError` at all, but should. In the latter case, the resulting `$page.error` will deviate from the [`App.Error`](types#Error) type, if it is specified.
SvelteKit 2 cleans this up by calling `handleError` hooks with two new properties: `status` and `message`. For errors thrown from your code (or library code called by your code) the status will be `500` and the message will be `Internal Error`. While `error.message` may contain sensitive information that should not be exposed to users, `message` is safe.
## Dynamic environment variables cannot be used during prerendering
The `$env/dynamic/public` and `$env/dynamic/private` modules provide access to _run time_ environment variables, as opposed to the _build time_ environment variables exposed by `$env/static/public` and `$env/static/private`.
During prerendering in SvelteKit 1, they are one and the same. This means that prerendered pages that make use of 'dynamic' environment variables are really 'baking in' build time values, which is incorrect. Worse, `$env/dynamic/public` is populated in the browser with these stale values if the user happens to land on a prerendered page before navigating to dynamically-rendered pages.
Because of this, dynamic environment variables can no longer be read during prerendering in SvelteKit 2 — you should use the `static` modules instead. If the user lands on a prerendered page, SvelteKit will request up-to-date values for `$env/dynamic/public` from the server (by default from a module called `/_app/env.js`) instead of reading them from the server-rendered HTML.
## `form` and `data` have been removed from `use:enhance` callbacks
If you provide a callback to [`use:enhance`](form-actions#Progressive-enhancement-use:enhance), it will be called with an object containing various useful properties.
In SvelteKit 1, those properties included `form` and `data`. These were deprecated some time ago in favour of `formElement` and `formData`, and have been removed altogether in SvelteKit 2.
## Forms containing file inputs must use `multipart/form-data`
If a form contains an `<input type="file">` but does not have an `enctype="multipart/form-data"` attribute, non-JS submissions will omit the file. SvelteKit 2 will throw an error if it encounters a form like this during a `use:enhance` submission to ensure that your forms work correctly when JavaScript is not present.
## Generated `tsconfig.json` is more strict
Previously, the generated `tsconfig.json` was trying its best to still produce a somewhat valid config when your `tsconfig.json` included `paths` or `baseUrl`. In SvelteKit 2, the validation is more strict and will warn when you use either `paths` or `baseUrl` in your `tsconfig.json`. These settings are used to generate path aliases and you should use [the `alias` config](configuration#alias) option in your `svelte.config.js` instead, to also create a corresponding alias for the bundler.
## `getRequest` no longer throws errors
The `@sveltejs/kit/node` module exports helper functions for use in Node environments, including `getRequest` which turns a Node [`ClientRequest`](https://nodejs.org/api/http.html#class-httpclientrequest) into a standard [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) object.
In SvelteKit 1, `getRequest` could throw if the `Content-Length` header exceeded the specified size limit. In SvelteKit 2, the error will not be thrown until later, when the request body (if any) is being read. This enables better diagnostics and simpler code.
## `vitePreprocess` is no longer exported from `@sveltejs/kit/vite`
Since `@sveltejs/vite-plugin-svelte` is now a peer dependency, SvelteKit 2 no longer re-exports `vitePreprocess`. You should import it directly from `@sveltejs/vite-plugin-svelte`.
## Updated dependency requirements
SvelteKit 2 requires Node `18.13` or higher, and the following minimum dependency versions:
- `svelte@4`
- `vite@5`
- `typescript@5`
- `@sveltejs/vite-plugin-svelte@3` (this is now required as a `peerDependency` of SvelteKit — previously it was directly depended upon)
- `@sveltejs/adapter-cloudflare@3` (if you're using these adapters)
- `@sveltejs/adapter-cloudflare-workers@2`
- `@sveltejs/adapter-netlify@3`
- `@sveltejs/adapter-node@2`
- `@sveltejs/adapter-static@3`
- `@sveltejs/adapter-vercel@4`
`svelte-migrate` will update your `package.json` for you.
As part of the TypeScript upgrade, the generated `tsconfig.json` (the one your `tsconfig.json` extends from) now uses `"moduleResolution": "bundler"` (which is recommended by the TypeScript team, as it properly resolves types from packages with an `exports` map in package.json) and `verbatimModuleSyntax` (which replaces the existing `importsNotUsedAsValues ` and `preserveValueImports` flags — if you have those in your `tsconfig.json`, remove them. `svelte-migrate` will do this for you).
## SvelteKit 2.12: $app/stores deprecated
SvelteKit 2.12 introduced `$app/state` based on the [Svelte 5 runes API](/docs/svelte/what-are-runes). `$app/state` provides everything that `$app/stores` provides but with more flexibility as to where and how you use it. Most importantly, the `page` object is now fine-grained, e.g. updates to `page.state` will not invalidate `page.data` and vice-versa.
As a consequence, `$app/stores` is deprecated and subject to be removed in SvelteKit 3. We recommend [upgrading to Svelte 5](/docs/svelte/v5-migration-guide), if you haven't already, and then migrate away from `$app/stores`. Most of the replacements should be pretty simple: Replace the `$app/stores` import with `$app/state` and remove the `$` prefixes from the usage sites.
```svelte
<script>
---import { page } from '$app/stores';---
+++import { page } from '$app/state';+++
</script>
---{$page.data}---
+++{page.data}+++
```
Use `npx sv migrate app-state` to auto-migrate most of your `$app/stores` usages inside `.svelte` components.
# Sapper からの移行
SvelteKit は Sapper の後継であり、その設計の多くの要素を共有しています。
もし、既存の Sapper アプリを SvelteKit に移行する予定がある場合、いくつかの変更が必要になります。移行する際には、[examples](additional-resources#Examples) を見ていただくと参考になると思います。
## package.json
### type: "module"
`package.json` に `"type": "module"` を追加します。もし Sapper 0.29.3 以降を使用している場合は、インクリメンタルマイグレーションの一部として、このステップを他のステップとは別に行うことができます。
### dependencies
`polka` や `express` を使用している場合はそれを削除し、`sirv` や `compression` などのミドルウェア(middleware)も削除します。
### devDependencies
`devDependencies` から `sapper` を削除し、`@sveltejs/kit` と使用予定の [adapter](adapters)に置き換えます([次のセクション](migrating#Project-files-Configuration)をご覧ください)。
### scripts
`sapper` を参照しているスクリプトを全て更新します:
- `sapper build` は、Node [adapter](adapters) を使用した `vite build` に更新します
- `sapper export` は、static [adapter](adapters) を使用した `vite build` に更新します
- `sapper dev` は `vite dev` に更新します
- `node __sapper__/build` は `node build` に更新します
## プロジェクトファイル <!--Project-files-->
アプリの大部分を占める `src/routes` の中はそのままで大丈夫ですが、いくつかのプロジェクトファイルを移動または更新する必要があります。
### Configuration
[こちら](configuration)に記載されている通り、`webpack.config.js` または `rollup.config.js` を `svelte.config.js` に置き換えてください。Svelte の preprocessor オプション は `config.preprocess` に移動してください。
[adapter](adapters) を追加する必要があります。`sapper build` は [adapter-node](adapter-node) とおおよそ同じで、`sapper export` は [adapter-static](adapter-static) とおおよそ同じですが、デプロイ先のプラットフォーム向けにデザインされた adapter を使用するのも良いでしょう。
[Vite](https://vitejs.dev) では自動的に処理されないファイルタイプのプラグインを使用している場合は、Vite において同等なことを行う方法を探し、[Vite config](project-structure#Project-files-vite.config.js) に追加する必要があります。
### src/client.js
SvelteKit にはこのファイルに相当するものはありません。カスタムロジック(`sapper.start(...)` 以降) は、`+layout.svelte` ファイルで、`onMount` コールバック内に記述してくさい。
### src/server.js
`adapter-node` を使用する場合は、[custom server](adapter-node#Custom-server) がこれと同等のものです。それ以外の場合は、同等のものに該当するものはありません。なぜなら SvelteKit アプリはサーバーレス環境でも実行可能だからです。
### src/service-worker.js
`@sapper/service-worker` からインポートするほとんどのものは、[`$service-worker`]($service-worker) に同等なものがあります:
- `files` は変更されていません
- `routes` は削除されました
- `shell` は現在 `build` になりました
- `timestamp` は現在 `version` になりました
### src/template.html
`src/template.html` は `src/app.html` にリネームする必要があります。
`%sapper.base%`、`%sapper.scripts%`、`%sapper.styles%` を削除します。`%sapper.head%` を `%sveltekit.head%` に、`%sapper.html%` を `%sveltekit.body%` にそれぞれ置き換えます。`<div id="sapper">` はもう必要ありません。
### src/node_modules
Sapper アプリでよくあるパターンとして、内部ライブラリを `src/node_modules` 内のディレクトリに配置する、というものがあります。これは Vite だと動作しないため、代わりに [`src/lib`]($lib) を使用します。
## ページとレイアウト <!--Pages-and-layouts-->
### 名前が変わったファイル <!--Renamed-files-->
ルート(Routes)は曖昧さをなくすためフォルダ名のみで構成されるようになり、`+page.svelte` までのフォルダ名がルート(route)に対応するようになりました。概要は [ルーティングのドキュメント](routing) をご参照ください。以下は 新/旧 のルーティング構造の比較です:
| Old | New |
| ------------------------- | ------------------------- |
| routes/about/index.svelte | routes/about/+page.svelte |
| routes/about.svelte | routes/about/+page.svelte |
カスタムのエラーページコンポーネントは `_error.svelte` から `+error.svelte` にリネームしてください。また、どの `_layout.svelte` ファイルも、同様に `+layout.svelte` にリネームしてください。[その他のファイルは無視されます](routing#Other-files).
### Imports
`@sapper/app` からインポートしていた `goto`、`prefetch`、`prefetchRoutes` は、[`$app/navigation`]($app-navigation) からインポートする `goto`、`preloadData`、`preloadCode` にそれぞれ置き換えてください。
`@sapper/app` からインポートしていた `stores` については置き換える必要があります — 以下の [Stores](migrating#Pages-and-layouts-Stores) をご覧ください。
`src/node_modules` にあるディレクトリからインポートしてたファイルは、[`$lib`]($lib) からのインポートに置き換えてください。
### Preload
以前と同様に、ページやレイアウトではレンダリングが行われる前にデータをロードできる関数をエクスポートすることができます。
This function has been renamed from `preload` to [`load`](load), it now lives in a `+page.js` (or `+layout.js`) next to its `+page.svelte` (or `+layout.svelte`), and its API has changed. Instead of two arguments — `page` and `session` — there is a single `event` argument.
There is no more `this` object, and consequently no `this.fetch`, `this.error` or `this.redirect`. Instead, you can get [`fetch`](load#Making-fetch-requests) from the input methods, and both [`error`](load#Errors) and [`redirect`](load#Redirects) are now thrown.
### Stores
Sapper では、提供されるストアをこのように参照していたかと思います:
```js
// @filename: ambient.d.ts
declare module '@sapper/app';
// @filename: index.js
// ---cut---
import { stores } from '@sapper/app';
const { preloading, page, session } = stores();
```
`page` と `session` ストアはまだ存在しています。`preloading` は、`from` プロパティと `to` プロパティを含む `navigating` ストアに置き換えられました。`page` は `url`、`params` を持つようになりましたが、`path` と `query` はありません。
SvelteKit では、それらにアクセスする方法が異なります。`stores` は `getStores` になりましたが、[`$app/stores`]($app-stores) から直接 `navigating`、`page`、`session` をインポートできるので、ほとんどの場合は必要ありません。もしあなたが Svelte 5 と SvelteKit 2.12 以上をお使いなら、代わりに [`$app/state`]($app-state) の使用を検討してみてください。
### ルーティング <!--Routing-->
ルート(routes) の正規表現はもうサポートされていません。代わりに、[advanced route matching](advanced-routing#Matching) をお使いください。
### Segments
以前までは、レイアウトコンポーネントは子のセグメントを表す `segment` プロパティを受け取っていましたが、この機能は削除されました。より柔軟な `$page.url.pathname` (や `page.url.pathname`) の値を使用し、お望みのセグメントを取得してください。
### URLs
Sapper では、相対 URL は、現在のページに対してではなく、base URL (`basepath` オプションが使用されていない限り、大抵の場合は `/`) に対して解決されていました。
これによって問題が発生していましたが、SvelteKit ではもうそのようなことはありません。相対 URL が現在のページ (または `load` 関数の `fetch` URL の場合は移動先のページ) に対して解決されるようになりました。多くの場合、(例えば、`/` 始まるような) ルート相対な URL を使用するほうが簡単です。なぜなら、それらの意図がコンテキストに依存しないからです。
### <a> attributes
- `sapper:prefetch` は `data-sveltekit-preload-data` になりました
- `sapper:noscroll` は `data-sveltekit-noscroll` になりました
## Endpoints
Sapper では、[サーバールート(server routes)](routing#server) は、Node の `http` モジュール によって公開される `req` と `res` オブジェクト(または Polka や Express などのフレームワークが提供するその拡張版) を受け取っていました。
SvelteKit は、アプリが動作する場所に依存しないように設計されています(Node サーバーで動作し、サーバーレスプラットフォームや Cloudflare Worker でも同様に動作します)。そのため、もう `req` と `res` を直接扱いません。エンドポイントを、新しいシグネチャに合わせて更新する必要があります。
環境非依存な動作をサポートするため、グローバルコンテキストで `fetch` が利用できるようになり、`node-fetch` や `cross-fetch` などのサーバーサイドの fetch 実装をインポートする必要がなくなりました。
## インテグレーション <!--Integrations-->
インテグレーションに関する詳細情報については [インテグレーション](./integrations) をご参照ください。
### HTML minifier
Sapper はデフォルトで `html-minifier` を含んでいました。SvelteKit はこれを含まないのですが、本番環境向けの依存関係(prod dependency)としてこれを追加し、[hook](hooks#Server-hooks-handle) で使用することができます:
```js
// @filename: ambient.d.ts
/// <reference types="@sveltejs/kit" />
declare module 'html-minifier';
// @filename: index.js
// ---cut---
import { minify } from 'html-minifier';
import { building } from '$app/environment';
const minification_options = {
collapseBooleanAttributes: true,
collapseWhitespace: true,
conservativeCollapse: true,
decodeEntities: true,
html5: true,
ignoreCustomComments: [/^#/],
minifyCSS: true,
minifyJS: false,
removeAttributeQuotes: true,
removeComments: false, // some hydration code needs comments, so leave them in
removeOptionalTags: true,
removeRedundantAttributes: true,
removeScriptTypeAttributes: true,
removeStyleLinkTypeAttributes: true,
sortAttributes: true,
sortClassName: true
};
/** @type {import('@sveltejs/kit').Handle} */
export async function handle({ event, resolve }) {
let page = '';
return resolve(event, {
transformPageChunk: ({ html, done }) => {
page += html;
if (done) {
return building ? minify(page, minification_options) : page;
}
}
});
}
```
サイトのプロダクションビルドをテストするのに `vite preview` を使用しているときは、`prerendering` が `false` となることにご注意ください。そのため、minify の結果を検証するには、ビルド済の HTML を直接確認する必要があります。
# Additional resources
## FAQs
よくある問題の解決方法や役に立つ tips や tricks については、[SvelteKit FAQ](faq) をご覧ください。
[Svelte FAQ](../svelte/faq) と [`vite-plugin-svelte` FAQ](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/faq.md) も、これらのライブラリに起因する疑問点には役立つでしょう。
## Examples
例として、数種類 SvelteKit サイトを作成し、公開しています:
- [`sveltejs/realworld`](https://github.com/sveltejs/realworld) contains an example blog site
- [A HackerNews clone](https://github.com/sveltejs/sites/tree/master/sites/hn.svelte.dev)
- [`svelte.dev`](https://github.com/sveltejs/svelte.dev)
また、SvelteKit ユーザーが GitHub で [#sveltekit](https://github.com/topics/sveltekit) や [#sveltekit-template](https://github.com/topics/sveltekit-template) というトピックを付けて多くの例を公開しており、[Svelte Society のサイト](https://sveltesociety.dev/recipe/sveltekit-templates-and-examples-e789ed397e7f38fc) にも例が公開されています。ただし、これらは Svelte 側のメンテナーによって検証されておらず、最新ではない可能性もありますのでご注意ください。
## サポート <!--Support-->
[Discord](/chat) や [StackOverflow](https://stackoverflow.com/questions/tagged/sveltekit) でヘルプを求めることができます。他の方の時間を尊重するため、まずは FAQ、Googleまたは他の検索エンジン、issue tracker、Discord のチャット履歴などから、問題に関連する情報を検索してください。回答する方より質問する方のほうが多いので、こうすることでコミュニティをスケーラブルに発展させることができると思います。
> 日本語翻訳版 追記：上記のDiscordはSvelte本体のもので、英語でコミュニケーションが行われています。もし日本語で質問したり交流したいのであれば、[Svelte日本のDiscord](https://discord.com/invite/YTXq3ZtBbx)にどうぞ！
# Glossary
SvelteKitのコアは、高度に設定可能(configurable)なレンダリングエンジンを提供します。このセクションでは、レンダリングについてディスカッションする際に使用されるいくつかの用語を説明します。これらのオプションを設定するためのリファレンスは、上記のドキュメントで提供されています。
## CSR
クライアントサイドレンダリング(Client-side rendering (CSR))とは、JavaScriptを使用してWebブラウザ上でページコンテンツを生成することです。
SvelteKit では、デフォルトでクライアントサイドレンダリングが使用されますが、[`csr = false` ページオプション](page-options#csr)で JavaScript をオフにすることができます。
## Edge
Rendering on the edge refers to rendering an application in a content delivery network (CDN) near the user. Edge rendering allows the request and response for a page to travel a shorter distance thus improving latency.
## Hybrid app
SvelteKit uses a hybrid rendering mode by default where it loads the initial HTML from the server (SSR), and then updates the page contents on subsequent navigations via client-side rendering (CSR).
## ハイドレーション(Hydration) <!--Hydration-->
Svelte コンポーネントは、何らかの状態を保存し、状態が更新されると DOM を更新します。SSR 中にデータをフェッチするとき、デフォルトでは SvelteKit はこのデータを保存し、サーバーレンダリングされた HTML と一緒にクライアントに送信します。それからコンポーネントは、同じ API エンドポイントを再度呼び出すことなく、クライアント側でそのデータを使用して初期化されます。そして Svelte はハイドレーション(Hydration)と呼ばれるプロセスで DOM が想定通りの状態にあることをチェックしてイベントリスナーをアタッチします。コンポーネントが完全にハイドレートされると、新しく作成された Svelte コンポーネントと同じように、プロパティの変更に反応(react)することができます。
SvelteKit では、デフォルトでページがハイドレーションされますが、[`csr = false` ページオプション](page-options#csr)で JavaScript をオフにすることができます。
## ISR
Incremental static regeneration (ISR) allows you to generate static pages on your site as visitors request those pages without redeploying. This may reduces build times compared to [SSG](#SSG) sites with a large number of pages. You can do [ISR with `adapter-vercel`](adapter-vercel#Incremental-Static-Regeneration).
## MPA
Traditional applications that render each page view on the server — such as those written in languages other than JavaScript — are often referred to as multi-page apps (MPA).
## プリレンダリング <!--Prerendering-->
プリレンダリング(Prerendering)とは、ビルド時にページのコンテンツを計算し、表示のために HTML を保存しておくことを意味します。このアプローチは旧来のサーバーレンダリングページと同じ利点を持ちつつ、訪問者ごとにページを再計算する必要がないため、訪問者数の増加に対してほぼ無償でスケールします。トレードオフとしては、ビルドプロセスのコストがより高くなり、プリレンダリングされたコンテンツはアプリケーションの新しいバージョンをデプロイすることでしか更新できなくなります。
「コンテンツがプリレンダリング可能である」というのは、それを直接表示する2人のユーザーが、サーバーから同じコンテンツを取得でき、かつ、そのページには [actions](form-actions) が含まれていない、ということです。全てのユーザーが同じプリレンダリングコンテンツを見ることができるのであれば、ページのパラメータに基づいてロードされるコンテンツはプリレンダリングが可能です。全てのページをプリレンダリングすることは、[Static Site Generation](#SSG)とも呼ばれます。
プリレンダリングされるページは静的なコンテンツに限りません。クライアントサイドでユーザ固有のデータをフェッチしてレンダリングする場合は、パーソナライズされたページを構築することができます。ただし、前述の通り、そのコンテンツに対して SSR を行わないことによるデメリットが発生することにご注意ください。
SvelteKit では、[`prerender` ページオプション](page-options#prerender) と、`svelte.config.js` の [`prerender` コンフィグ](configuration#prerender) によってプリレンダリングをコントロールできます。
## PWA
A progressive web app (PWA) is an app that's built using web APIs and technologies, but functions like a mobile or desktop app. Sites served as [PWAs can be installed](https://web.dev/learn/pwa/installation), allowing you to add a shortcut to the application on your launcher, home screen, or start menu. Many PWAs will utilize [service workers](service-workers) to build offline capabilities.
## ルーティング <!--Routing-->
デフォルトでは、(リンクをクリックしたりブラウザの 進む または 戻る ボタンを使って)新しいページにナビゲートするとき、SvelteKit はナビゲーションをインターセプトし、ブラウザが移動先のページのリクエストをサーバーにリクエストする代わりに、それを処理します。それから SvelteKit は新しいページのコンポーネントをレンダリングし、そのときに順番に必要な API エンドポイントをコールし、クライアントの表示コンテンツを更新します。このような、ナビゲーションが行われる際にそれに応じてクライアント側でページを更新するプロセスのことを、クライアントサイドルーティングと呼びます。
SvelteKit では、デフォルトでクライアントサイドルーティングが使用されますが、[`data-sveltekit-reload`](link-options#data-sveltekit-reload) でこれをスキップすることができます。
## SPA
シングルページアプリ(single-page app (SPA))とは、サーバーへの全てのリクエストで単一のHTMLをロードし、クライアントサイドレンダリングをリクエストされたURLに基づいて行うアプリケーションのことです。全てのナビゲーションはクライアントサイドで(クライアントサイドルーティングと呼ばれるプロセスで)処理され、ページごとのコンテンツは更新されるが共通のレイアウト要素はほとんど更新されません。このサイト全体で、SPAを指すときは、初期リクエストの際に空のシェルを返すという定義を使用しています。初期リクエストで HTML を提供する[ハイブリッドアプリ](#Hybrid-app)と混同しないでください。SPA モードでは、レンダリングが開始される前に2つのネットワークラウンドトリップが必要になるため、パフォーマンスに大きな影響を与えます。SPA モードはパフォーマンスと SEO に大きな悪影響を与えるため、モバイルアプリにラップされる場合など、ごく限られた状況でのみ推奨されます。
SvelteKit では、[`adapter-static` を使って SPA を構築](single-page-apps) することができます。
## SSG
静的サイト生成(Static Site Generation (SSG))とは、全てのページがプリレンダリングされているサイトを指す用語です。サイトを完全にプリレンダリングすることの利点の1つは、SSRを実行するためのサーバーを維持したり費用を払ったりする必要がないことです。一度生成すれば、そのサイトは CDN から提供することができ、"time to first byte" の優れたパフォーマンスにつながります。このデリバリーモデルはしばしば JAMstack と呼ばれます。
In SvelteKit, you can do static site generation by using [`adapter-static`](adapter-static) or by configuring every page to be [prerendered](#Prerendering) using [the `prerender` page option](page-options#prerender) or [`prerender` config](configuration#prerender) in `svelte.config.js`.
## SSR
サーバーサイドレンダリング(Server-side rendering (SSR))とは、サーバー上でページコンテンツを生成することです。SSR やプリレンダリングによってサーバーからページコンテンツを返すことは、パフォーマンスと SEO の観点で非常に望ましいです。SPA で必要となる余分なラウンドトリップを回避することでパフォーマンスが大幅に向上し、また、JavaScript が失敗したり無効にされている場合でも、ユーザーがアプリにアクセスできるようになります (実際、JavaScript が動作しない状況は[想像以上に頻繁に発生します](https://kryogenix.org/code/browser/everyonehasjs.html))。一部の検索エンジンはクライアントサイドで動的に生成されたコンテンツをインデックスできますが、その場合でも時間がかかる可能性があります。
SvelteKit では、デフォルトでページがサーバーサイドレンダリングされます。[`ssr` ページオプション](page-options#ssr) で SSR を無効化できます。
# @sveltejs/kit
```js
// @noErrors
import {
Server,
VERSION,
error,
fail,
invalid,
isActionFailure,
isHttpError,
isRedirect,
isValidationError,
json,
normalizeUrl,
redirect,
text
} from '@sveltejs/kit';
```
## Server
<div class="ts-block">
```dts
class Server {/*…*/}
```
<div class="ts-block-property">
```dts
constructor(manifest: SSRManifest);
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
init(options: ServerInitOptions): Promise<void>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
respond(request: Request, options: RequestOptions): Promise<Response>;
```
<div class="ts-block-property-details"></div>
</div></div>
## VERSION
<div class="ts-block">
```dts
const VERSION: string;
```
</div>
## error
Throws an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response without invoking `handleError`.
Make sure you're not catching the thrown error, which would prevent SvelteKit from handling it.
<div class="ts-block">
```dts
function error(status: number, body: App.Error): never;
```
</div>
<div class="ts-block">
```dts
function error(
status: number,
body?: {
message: string;
} extends App.Error
? App.Error | string | undefined
: never
): never;
```
</div>
## fail
Create an `ActionFailure` object. Call when form submission fails.
<div class="ts-block">
```dts
function fail(status: number): ActionFailure<undefined>;
```
</div>
<div class="ts-block">
```dts
function fail<T = undefined>(
status: number,
data: T
): ActionFailure<T>;
```
</div>
## invalid
<blockquote class="since note">
Available since 2.47.3
</blockquote>
Use this to throw a validation error to imperatively fail form validation.
Can be used in combination with `issue` passed to form actions to create field-specific issues.
```ts
import { invalid } from '@sveltejs/kit';
import { form } from '$app/server';
import { tryLogin } from '$lib/server/auth';
import * as v from 'valibot';
export const login = form(
v.object({ name: v.string(), _password: v.string() }),
async ({ name, _password }) => {
const success = tryLogin(name, _password);
if (!success) {
invalid('Incorrect username or password');
}
// ...
}
);
```
<div class="ts-block">
```dts
function invalid(
...issues: (StandardSchemaV1.Issue | string)[]
): never;
```
</div>
## isActionFailure
Checks whether this is an action failure thrown by `fail`.
<div class="ts-block">
```dts
function isActionFailure(e: unknown): e is ActionFailure;
```
</div>
## isHttpError
Checks whether this is an error thrown by `error`.
<div class="ts-block">
```dts
function isHttpError<T extends number>(
e: unknown,
status?: T
): e is HttpError_1 & {
status: T extends undefined ? never : T;
};
```
</div>
## isRedirect
Checks whether this is a redirect thrown by `redirect`.
<div class="ts-block">
```dts
function isRedirect(e: unknown): e is Redirect_1;
```
</div>
## isValidationError
<blockquote class="since note">
Available since 2.47.3
</blockquote>
Checks whether this is an validation error thrown by `invalid`.
<div class="ts-block">
```dts
function isValidationError(e: unknown): e is ActionFailure;
```
</div>
## json
Create a JSON `Response` object from the supplied data.
<div class="ts-block">
```dts
function json(data: any, init?: ResponseInit): Response;
```
</div>
## normalizeUrl
<blockquote class="since note">
Available since 2.18.0
</blockquote>
Strips possible SvelteKit-internal suffixes and trailing slashes from the URL pathname.
Returns the normalized URL as well as a method for adding the potential suffix back
based on a new pathname (possibly including search) or URL.
```js
// @errors: 7031
import { normalizeUrl } from '@sveltejs/kit';
const { url, denormalize } = normalizeUrl('/blog/post/__data.json');
console.log(url.pathname); // /blog/post
console.log(denormalize('/blog/post/a')); // /blog/post/a/__data.json
```
<div class="ts-block">
```dts
function normalizeUrl(url: URL | string): {
url: URL;
wasNormalized: boolean;
denormalize: (url?: string | URL) => URL;
};
```
</div>
## redirect
Redirect a request. When called during request handling, SvelteKit will return a redirect response.
Make sure you're not catching the thrown redirect, which would prevent SvelteKit from handling it.
Most common status codes:
* `303 See Other`: redirect as a GET request (often used after a form POST request)
* `307 Temporary Redirect`: redirect will keep the request method
* `308 Permanent Redirect`: redirect will keep the request method, SEO will be transferred to the new page
[See all redirect status codes](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status#redirection_messages)
<div class="ts-block">
```dts
function redirect(
status:
| 300
| 301
| 302
| 303
| 304
| 305
| 306
| 307
| 308
| ({} & number),
location: string | URL
): never;
```
</div>
## text
Create a `Response` object from the supplied body.
<div class="ts-block">
```dts
function text(body: string, init?: ResponseInit): Response;
```
</div>
## Action
Shape of a form action method that is part of `export const actions = {...}` in `+page.server.js`.
See [form actions](/docs/kit/form-actions) for more information.
<div class="ts-block">
```dts
type Action<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends AppRouteId | null = AppRouteId | null
> = (
event: RequestEvent<Params, RouteId>
) => MaybePromise<OutputData>;
```
</div>
## ActionFailure
<div class="ts-block">
```dts
interface ActionFailure<T = undefined> {/*…*/}
```
<div class="ts-block-property">
```dts
status: number;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
data: T;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
[uniqueSymbol]: true;
```
<div class="ts-block-property-details"></div>
</div></div>
## ActionResult
When calling a form action via fetch, the response will be one of these shapes.
```svelte
<form method="post" use:enhance={() => {
return ({ result }) => {
// result is of type ActionResult
};
}}
```
<div class="ts-block">
```dts
type ActionResult<
Success extends Record<string, unknown> | undefined =
Record<string, any>,
Failure extends Record<string, unknown> | undefined =
Record<string, any>
> =
| { type: 'success'; status: number; data?: Success }
| { type: 'failure'; status: number; data?: Failure }
| { type: 'redirect'; status: number; location: string }
| { type: 'error'; status?: number; error: any };
```
</div>
## Actions
Shape of the `export const actions = {...}` object in `+page.server.js`.
See [form actions](/docs/kit/form-actions) for more information.
<div class="ts-block">
```dts
type Actions<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends AppRouteId | null = AppRouteId | null
> = Record<string, Action<Params, OutputData, RouteId>>;
```
</div>
## Adapter
[Adapters](/docs/kit/adapters) are responsible for taking the production build and turning it into something that can be deployed to a platform of your choosing.
<div class="ts-block">
```dts
interface Adapter {/*…*/}
```
<div class="ts-block-property">
```dts
name: string;
```
<div class="ts-block-property-details">
The name of the adapter, using for logging. Will typically correspond to the package name.
</div>
</div>
<div class="ts-block-property">
```dts
adapt: (builder: Builder) => MaybePromise<void>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `builder` An object provided by SvelteKit that contains methods for adapting the app
</div>
This function is called after SvelteKit has built your app.
</div>
</div>
<div class="ts-block-property">
```dts
supports?: {/*…*/}
```
<div class="ts-block-property-details">
Checks called during dev and build to determine whether specific features will work in production with this adapter.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
read?: (details: { config: any; route: { id: string } }) => boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `details.config` The merged adapter-specific route config exported from the route with `export const config`
</div>
Test support for `read` from `$app/server`.
</div>
</div>
<div class="ts-block-property">
```dts
instrumentation?: () => boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag since">available since</span> v2.31.0
</div>
Test support for `instrumentation.server.js`. To pass, the adapter must support running `instrumentation.server.js` prior to the application code.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
emulate?: () => MaybePromise<Emulator>;
```
<div class="ts-block-property-details">
Creates an `Emulator`, which allows the adapter to influence the environment
during dev, build and prerendering.
</div>
</div></div>
## AfterNavigate
The argument passed to [`afterNavigate`](/docs/kit/$app-navigation#afterNavigate) callbacks.
<div class="ts-block">
```dts
type AfterNavigate = (Navigation | NavigationEnter) & {
type: Exclude<NavigationType, 'leave'>;
/**
* Since `afterNavigate` callbacks are called after a navigation completes, they will never be called with a navigation that unloads the page.
*/
willUnload: false;
};
```
</div>
## AwaitedActions
<div class="ts-block">
```dts
type AwaitedActions<
T extends Record<string, (...args: any) => any>
> = OptionalUnion<
{
[Key in keyof T]: UnpackValidationError<
Awaited<ReturnType<T[Key]>>
>;
}[keyof T]
>;
```
</div>
## BeforeNavigate
The argument passed to [`beforeNavigate`](/docs/kit/$app-navigation#beforeNavigate) callbacks.
<div class="ts-block">
```dts
type BeforeNavigate = Navigation & {
/**
* Call this to prevent the navigation from starting.
*/
cancel: () => void;
};
```
</div>
## Builder
This object is passed to the `adapt` function of adapters.
It contains various methods and properties that are useful for adapting the app.
<div class="ts-block">
```dts
interface Builder {/*…*/}
```
<div class="ts-block-property">
```dts
log: Logger;
```
<div class="ts-block-property-details">
Print messages to the console. `log.info` and `log.minor` are silent unless Vite's `logLevel` is `info`.
</div>
</div>
<div class="ts-block-property">
```dts
rimraf: (dir: string) => void;
```
<div class="ts-block-property-details">
Remove `dir` and all its contents.
</div>
</div>
<div class="ts-block-property">
```dts
mkdirp: (dir: string) => void;
```
<div class="ts-block-property-details">
Create `dir` and any required parent directories.
</div>
</div>
<div class="ts-block-property">
```dts
config: ValidatedConfig;
```
<div class="ts-block-property-details">
The fully resolved Svelte config.
</div>
</div>
<div class="ts-block-property">
```dts
prerendered: Prerendered;
```
<div class="ts-block-property-details">
Information about prerendered pages and assets, if any.
</div>
</div>
<div class="ts-block-property">
```dts
routes: RouteDefinition[];
```
<div class="ts-block-property-details">
An array of all routes (including prerendered)
</div>
</div>
<div class="ts-block-property">
```dts
createEntries: (fn: (route: RouteDefinition) => AdapterEntry) => Promise<void>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `fn` A function that groups a set of routes into an entry point
- <span class="tag deprecated">deprecated</span> Use `builder.routes` instead
</div>
Create separate functions that map to one or more routes of your app.
</div>
</div>
<div class="ts-block-property">
```dts
findServerAssets: (routes: RouteDefinition[]) => string[];
```
<div class="ts-block-property-details">
Find all the assets imported by server files belonging to `routes`
</div>
</div>
<div class="ts-block-property">
```dts
generateFallback: (dest: string) => Promise<void>;
```
<div class="ts-block-property-details">
Generate a fallback page for a static webserver to use when no route is matched. Useful for single-page apps.
</div>
</div>
<div class="ts-block-property">
```dts
generateEnvModule: () => void;
```
<div class="ts-block-property-details">
Generate a module exposing build-time environment variables as `$env/dynamic/public`.
</div>
</div>
<div class="ts-block-property">
```dts
generateManifest: (opts: { relativePath: string; routes?: RouteDefinition[] }) => string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `opts` a relative path to the base directory of the app and optionally in which format (esm or cjs) the manifest should be generated
</div>
Generate a server-side manifest to initialise the SvelteKit [server](/docs/kit/@sveltejs-kit#Server) with.
</div>
</div>
<div class="ts-block-property">
```dts
getBuildDirectory: (name: string) => string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` path to the file, relative to the build directory
</div>
Resolve a path to the `name` directory inside `outDir`, e.g. `/path/to/.svelte-kit/my-adapter`.
</div>
</div>
<div class="ts-block-property">
```dts
getClientDirectory: () => string;
```
<div class="ts-block-property-details">
Get the fully resolved path to the directory containing client-side assets, including the contents of your `static` directory.
</div>
</div>
<div class="ts-block-property">
```dts
getServerDirectory: () => string;
```
<div class="ts-block-property-details">
Get the fully resolved path to the directory containing server-side code.
</div>
</div>
<div class="ts-block-property">
```dts
getAppPath: () => string;
```
<div class="ts-block-property-details">
Get the application path including any configured `base` path, e.g. `my-base-path/_app`.
</div>
</div>
<div class="ts-block-property">
```dts
writeClient: (dest: string) => string[];
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `dest` the destination folder
- <span class="tag">returns</span> an array of files written to `dest`
</div>
Write client assets to `dest`.
</div>
</div>
<div class="ts-block-property">
```dts
writePrerendered: (dest: string) => string[];
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `dest` the destination folder
- <span class="tag">returns</span> an array of files written to `dest`
</div>
Write prerendered files to `dest`.
</div>
</div>
<div class="ts-block-property">
```dts
writeServer: (dest: string) => string[];
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `dest` the destination folder
- <span class="tag">returns</span> an array of files written to `dest`
</div>
Write server-side code to `dest`.
</div>
</div>
<div class="ts-block-property">
```dts
copy: (
from: string,
to: string,
opts?: {
filter?(basename: string): boolean;
replace?: Record<string, string>;
}
) => string[];
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `from` the source file or directory
- `to` the destination file or directory
- `opts.filter` a function to determine whether a file or directory should be copied
- `opts.replace` a map of strings to replace
- <span class="tag">returns</span> an array of files that were copied
</div>
Copy a file or directory.
</div>
</div>
<div class="ts-block-property">
```dts
hasServerInstrumentationFile: () => boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">returns</span> true if the server instrumentation file exists, false otherwise
- <span class="tag since">available since</span> v2.31.0
</div>
Check if the server instrumentation file exists.
</div>
</div>
<div class="ts-block-property">
```dts
instrument: (args: {
entrypoint: string;
instrumentation: string;
start?: string;
module?:
| {
exports: string[];
}
| {
generateText: (args: { instrumentation: string; start: string }) => string;
};
}) => void;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `options` an object containing the following properties:
- `options.entrypoint` the path to the entrypoint to trace.
- `options.instrumentation` the path to the instrumentation file.
- `options.start` the name of the start file. This is what `entrypoint` will be renamed to.
- `options.module` configuration for the resulting entrypoint module.
- `options.module.generateText` a function that receives the relative paths to the instrumentation and start files, and generates the text of the module to be traced. If not provided, the default implementation will be used, which uses top-level await.
- <span class="tag since">available since</span> v2.31.0
</div>
Instrument `entrypoint` with `instrumentation`.
Renames `entrypoint` to `start` and creates a new module at
`entrypoint` which imports `instrumentation` and then dynamically imports `start`. This allows
the module hooks necessary for instrumentation libraries to be loaded prior to any application code.
Caveats:
- "Live exports" will not work. If your adapter uses live exports, your users will need to manually import the server instrumentation on startup.
- If `tla` is `false`, OTEL auto-instrumentation may not work properly. Use it if your environment supports it.
- Use `hasServerInstrumentationFile` to check if the user has a server instrumentation file; if they don't, you shouldn't do this.
</div>
</div>
<div class="ts-block-property">
```dts
compress: (directory: string) => Promise<void>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `directory` The directory containing the files to be compressed
</div>
Compress files in `directory` with gzip and brotli, where appropriate. Generates `.gz` and `.br` files alongside the originals.
</div>
</div></div>
## ClientInit
<blockquote class="since note">
Available since 2.10.0
</blockquote>
The [`init`](/docs/kit/hooks#Shared-hooks-init) will be invoked once the app starts in the browser
<div class="ts-block">
```dts
type ClientInit = () => MaybePromise<void>;
```
</div>
## Config
See the [configuration reference](/docs/kit/configuration) for details.
## Cookies
<div class="ts-block">
```dts
interface Cookies {/*…*/}
```
<div class="ts-block-property">
```dts
get: (name: string, opts?: import('cookie').CookieParseOptions) => string | undefined;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` the name of the cookie
- `opts` the options, passed directly to `cookie.parse`. See documentation [here](https://github.com/jshttp/cookie#cookieparsestr-options)
</div>
Gets a cookie that was previously set with `cookies.set`, or from the request headers.
</div>
</div>
<div class="ts-block-property">
```dts
getAll: (opts?: import('cookie').CookieParseOptions) => Array<{ name: string; value: string }>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `opts` the options, passed directly to `cookie.parse`. See documentation [here](https://github.com/jshttp/cookie#cookieparsestr-options)
</div>
Gets all cookies that were previously set with `cookies.set`, or from the request headers.
</div>
</div>
<div class="ts-block-property">
```dts
set: (
name: string,
value: string,
opts: import('cookie').CookieSerializeOptions & { path: string }
) => void;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` the name of the cookie
- `value` the cookie value
- `opts` the options, passed directly to `cookie.serialize`. See documentation [here](https://github.com/jshttp/cookie#cookieserializename-value-options)
</div>
Sets a cookie. This will add a `set-cookie` header to the response, but also make the cookie available via `cookies.get` or `cookies.getAll` during the current request.
The `httpOnly` and `secure` options are `true` by default (except on http://localhost, where `secure` is `false`), and must be explicitly disabled if you want cookies to be readable by client-side JavaScript and/or transmitted over HTTP. The `sameSite` option defaults to `lax`.
You must specify a `path` for the cookie. In most cases you should explicitly set `path: '/'` to make the cookie available throughout your app. You can use relative paths, or set `path: ''` to make the cookie only available on the current path and its children
</div>
</div>
<div class="ts-block-property">
```dts
delete: (name: string, opts: import('cookie').CookieSerializeOptions & { path: string }) => void;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` the name of the cookie
- `opts` the options, passed directly to `cookie.serialize`. The `path` must match the path of the cookie you want to delete. See documentation [here](https://github.com/jshttp/cookie#cookieserializename-value-options)
</div>
Deletes a cookie by setting its value to an empty string and setting the expiry date in the past.
You must specify a `path` for the cookie. In most cases you should explicitly set `path: '/'` to make the cookie available throughout your app. You can use relative paths, or set `path: ''` to make the cookie only available on the current path and its children
</div>
</div>
<div class="ts-block-property">
```dts
serialize: (
name: string,
value: string,
opts: import('cookie').CookieSerializeOptions & { path: string }
) => string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` the name of the cookie
- `value` the cookie value
- `opts` the options, passed directly to `cookie.serialize`. See documentation [here](https://github.com/jshttp/cookie#cookieserializename-value-options)
</div>
Serialize a cookie name-value pair into a `Set-Cookie` header string, but don't apply it to the response.
The `httpOnly` and `secure` options are `true` by default (except on http://localhost, where `secure` is `false`), and must be explicitly disabled if you want cookies to be readable by client-side JavaScript and/or transmitted over HTTP. The `sameSite` option defaults to `lax`.
You must specify a `path` for the cookie. In most cases you should explicitly set `path: '/'` to make the cookie available throughout your app. You can use relative paths, or set `path: ''` to make the cookie only available on the current path and its children
</div>
</div></div>
## Emulator
A collection of functions that influence the environment during dev, build and prerendering
<div class="ts-block">
```dts
interface Emulator {/*…*/}
```
<div class="ts-block-property">
```dts
platform?(details: { config: any; prerender: PrerenderOption }): MaybePromise<App.Platform>;
```
<div class="ts-block-property-details">
A function that is called with the current route `config` and `prerender` option
and returns an `App.Platform` object
</div>
</div></div>
## Handle
The [`handle`](/docs/kit/hooks#Server-hooks-handle) hook runs every time the SvelteKit server receives a [request](/docs/kit/web-standards#Fetch-APIs-Request) and
determines the [response](/docs/kit/web-standards#Fetch-APIs-Response).
It receives an `event` object representing the request and a function called `resolve`, which renders the route and generates a `Response`.
This allows you to modify response headers or bodies, or bypass SvelteKit entirely (for implementing routes programmatically, for example).
<div class="ts-block">
```dts
type Handle = (input: {
event: RequestEvent;
resolve: (
event: RequestEvent,
opts?: ResolveOptions
) => MaybePromise<Response>;
}) => MaybePromise<Response>;
```
</div>
## HandleClientError
The client-side [`handleError`](/docs/kit/hooks#Shared-hooks-handleError) hook runs when an unexpected error is thrown while navigating.
If an unexpected error is thrown during loading or the following render, this function will be called with the error and the event.
Make sure that this function _never_ throws an error.
<div class="ts-block">
```dts
type HandleClientError = (input: {
error: unknown;
event: NavigationEvent;
status: number;
message: string;
}) => MaybePromise<void | App.Error>;
```
</div>
## HandleFetch
The [`handleFetch`](/docs/kit/hooks#Server-hooks-handleFetch) hook allows you to modify (or replace) the result of an [`event.fetch`](/docs/kit/load#Making-fetch-requests) call that runs on the server (or during prerendering) inside an endpoint, `load`, `action`, `handle`, `handleError` or `reroute`.
<div class="ts-block">
```dts
type HandleFetch = (input: {
event: RequestEvent;
request: Request;
fetch: typeof fetch;
}) => MaybePromise<Response>;
```
</div>
## HandleServerError
The server-side [`handleError`](/docs/kit/hooks#Shared-hooks-handleError) hook runs when an unexpected error is thrown while responding to a request.
If an unexpected error is thrown during loading or rendering, this function will be called with the error and the event.
Make sure that this function _never_ throws an error.
<div class="ts-block">
```dts
type HandleServerError = (input: {
error: unknown;
event: RequestEvent;
status: number;
message: string;
}) => MaybePromise<void | App.Error>;
```
</div>
## HandleValidationError
The [`handleValidationError`](/docs/kit/hooks#Server-hooks-handleValidationError) hook runs when the argument to a remote function fails validation.
It will be called with the validation issues and the event, and must return an object shape that matches `App.Error`.
<div class="ts-block">
```dts
type HandleValidationError<
Issue extends StandardSchemaV1.Issue =
StandardSchemaV1.Issue
> = (input: {
issues: Issue[];
event: RequestEvent;
}) => MaybePromise<App.Error>;
```
</div>
## HttpError
The object returned by the [`error`](/docs/kit/@sveltejs-kit#error) function.
<div class="ts-block">
```dts
interface HttpError {/*…*/}
```
<div class="ts-block-property">
```dts
status: number;
```
<div class="ts-block-property-details">
The [HTTP status code](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status#client_error_responses), in the range 400-599.
</div>
</div>
<div class="ts-block-property">
```dts
body: App.Error;
```
<div class="ts-block-property-details">
The content of the error.
</div>
</div></div>
## InvalidField
A function and proxy object used to imperatively create validation errors in form handlers.
Access properties to create field-specific issues: `issue.fieldName('message')`.
The type structure mirrors the input data structure for type-safe field access.
Call `invalid(issue.foo(...), issue.nested.bar(...))` to throw a validation error.
<div class="ts-block">
```dts
type InvalidField<T> =
WillRecurseIndefinitely<T> extends true
? Record<string | number, any>
: NonNullable<T> extends
| string
| number
| boolean
| File
? (message: string) => StandardSchemaV1.Issue
: NonNullable<T> extends Array<infer U>
? {
[K in number]: InvalidField<U>;
} & ((message: string) => StandardSchemaV1.Issue)
: NonNullable<T> extends RemoteFormInput
? {
[K in keyof T]-?: InvalidField<T[K]>;
} & ((
message: string
) => StandardSchemaV1.Issue)
: Record<string, never>;
```
</div>
## KitConfig
See the [configuration reference](/docs/kit/configuration) for details.
## LessThan
<div class="ts-block">
```dts
type LessThan<
TNumber extends number,
TArray extends any[] = []
> = TNumber extends TArray['length']
? TArray[number]
: LessThan<TNumber, [...TArray, TArray['length']]>;
```
</div>
## LiveQueryRequestedResult
<div class="ts-block">
```dts
type LiveQueryRequestedResult<Validated, Output> = Iterable<
LiveRequestedEntry<Validated, Output>
> &
AsyncIterable<LiveRequestedEntry<Validated, Output>> & {
/**
* Call `reconnect` on all live queries selected by this `requested` invocation.
* This is identical to:
* ```ts
* import { requested } from '$app/server';
*
* for await (const { query } of requested(liveQuery, ...)) {
* void query.reconnect();
* }
* ```
*/
reconnectAll: () => Promise<void>;
};
```
</div>
## LiveRequestedEntry
A single entry yielded by [`requested`](/docs/kit/$app-server#requested)
when called with a `query.live`. `arg` is the validated argument; `query` is a
`RemoteLiveQuery` bound to the client's original cache key, so `reconnect()` targets
the correct client subscription.
<div class="ts-block">
```dts
type LiveRequestedEntry<Validated, Output> = {
arg: Validated;
query: RemoteLiveQuery<Output>;
};
```
</div>
## Load
The generic form of `PageLoad` and `LayoutLoad`. You should import those from `./$types` (see [generated types](/docs/kit/types#Generated-types))
rather than using `Load` directly.
<div class="ts-block">
```dts
type Load<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
InputData extends Record<string, unknown> | null = Record<
string,
any
> | null,
ParentData extends Record<string, unknown> = Record<
string,
any
>,
OutputData extends Record<string, unknown> | void =
Record<string, any> | void,
RouteId extends AppRouteId | null = AppRouteId | null
> = (
event: LoadEvent<Params, InputData, ParentData, RouteId>
) => MaybePromise<OutputData>;
```
</div>
## LoadEvent
The generic form of `PageLoadEvent` and `LayoutLoadEvent`. You should import those from `./$types` (see [generated types](/docs/kit/types#Generated-types))
rather than using `LoadEvent` directly.
<div class="ts-block">
```dts
interface LoadEvent<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
Data extends Record<string, unknown> | null = Record<
string,
any
> | null,
ParentData extends Record<string, unknown> = Record<
string,
any
>,
RouteId extends AppRouteId | null = AppRouteId | null
> extends NavigationEvent<Params, RouteId> {/*…*/}
```
<div class="ts-block-property">
```dts
fetch: typeof fetch;
```
<div class="ts-block-property-details">
`fetch` is equivalent to the [native `fetch` web API](https://developer.mozilla.org/en-US/docs/Web/API/fetch), with a few additional features:
- It can be used to make credentialed requests on the server, as it inherits the `cookie` and `authorization` headers for the page request.
- It can make relative requests on the server (ordinarily, `fetch` requires a URL with an origin when used in a server context).
- Internal requests (e.g. for `+server.js` routes) go directly to the handler function when running on the server, without the overhead of an HTTP call.
- During server-side rendering, the response will be captured and inlined into the rendered HTML by hooking into the `text` and `json` methods of the `Response` object. Note that headers will _not_ be serialized, unless explicitly included via [`filterSerializedResponseHeaders`](/docs/kit/hooks#Server-hooks-handle)
- During hydration, the response will be read from the HTML, guaranteeing consistency and preventing an additional network request.
You can learn more about making credentialed requests with cookies [here](/docs/kit/load#Cookies)
</div>
</div>
<div class="ts-block-property">
```dts
data: Data;
```
<div class="ts-block-property-details">
Contains the data returned by the route's server `load` function (in `+layout.server.js` or `+page.server.js`), if any.
</div>
</div>
<div class="ts-block-property">
```dts
setHeaders: (headers: Record<string, string>) => void;
```
<div class="ts-block-property-details">
If you need to set headers for the response, you can do so using the this method. This is useful if you want the page to be cached, for example:
```js
// @errors: 7031
/// file: src/routes/blog/+page.js
export async function load({ fetch, setHeaders }) {
const url = `https://cms.example.com/articles.json`;
const response = await fetch(url);
setHeaders({
age: response.headers.get('age'),
'cache-control': response.headers.get('cache-control')
});
return response.json();
}
```
Setting the same header multiple times (even in separate `load` functions) is an error — you can only set a given header once.
You cannot add a `set-cookie` header with `setHeaders` — use the [`cookies`](/docs/kit/@sveltejs-kit#Cookies) API in a server-only `load` function instead.
`setHeaders` has no effect when a `load` function runs in the browser.
</div>
</div>
<div class="ts-block-property">
```dts
parent: () => Promise<ParentData>;
```
<div class="ts-block-property-details">
`await parent()` returns data from parent `+layout.js` `load` functions.
Implicitly, a missing `+layout.js` is treated as a `({ data }) => data` function, meaning that it will return and forward data from parent `+layout.server.js` files.
Be careful not to introduce accidental waterfalls when using `await parent()`. If for example you only want to merge parent data into the returned output, call it _after_ fetching your other data.
</div>
</div>
<div class="ts-block-property">
```dts
depends: (...deps: Array<`${string}:${string}`>) => void;
```
<div class="ts-block-property-details">
This function declares that the `load` function has a _dependency_ on one or more URLs or custom identifiers, which can subsequently be used with [`invalidate()`](/docs/kit/$app-navigation#invalidate) to cause `load` to rerun.
Most of the time you won't need this, as `fetch` calls `depends` on your behalf — it's only necessary if you're using a custom API client that bypasses `fetch`.
URLs can be absolute or relative to the page being loaded, and must be [encoded](https://developer.mozilla.org/en-US/docs/Glossary/percent-encoding).
Custom identifiers have to be prefixed with one or more lowercase letters followed by a colon to conform to the [URI specification](https://www.rfc-editor.org/rfc/rfc3986.html).
The following example shows how to use `depends` to register a dependency on a custom identifier, which is `invalidate`d after a button click, making the `load` function rerun.
```js
// @errors: 7031
/// file: src/routes/+page.js
let count = 0;
export async function load({ depends }) {
depends('increase:count');
return { count: count++ };
}
```
```html
/// file: src/routes/+page.svelte
<script>
import { invalidate } from '$app/navigation';
let { data } = $props();
const increase = async () => {
await invalidate('increase:count');
}
</script>
<p>{data.count}<p>
<button on:click={increase}>Increase Count</button>
```
</div>
</div>
<div class="ts-block-property">
```dts
untrack: <T>(fn: () => T) => T;
```
<div class="ts-block-property-details">
Use this function to opt out of dependency tracking for everything that is synchronously called within the callback. Example:
```js
// @errors: 7031
/// file: src/routes/+page.server.js
export async function load({ untrack, url }) {
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}
```
</div>
</div>
<div class="ts-block-property">
```dts
tracing: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag since">available since</span> v2.31.0
</div>
Access to spans for tracing. If tracing is not enabled or the function is being run in the browser, these spans will do nothing.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
enabled: boolean;
```
<div class="ts-block-property-details">
Whether tracing is enabled.
</div>
</div>
<div class="ts-block-property">
```dts
root: Span;
```
<div class="ts-block-property-details">
The root span for the request. This span is named `sveltekit.handle.root`.
</div>
</div>
<div class="ts-block-property">
```dts
current: Span;
```
<div class="ts-block-property-details">
The span associated with the current `load` function.
</div>
</div></div>
</div>
</div></div>
## LoadProperties
<div class="ts-block">
```dts
type LoadProperties<
input extends Record<string, any> | void
> = input extends void
? undefined // needs to be undefined, because void will break intellisense
: input extends Record<string, any>
? input
: unknown;
```
</div>
## Navigation
<div class="ts-block">
```dts
type Navigation =
| NavigationExternal
| NavigationFormSubmit
| NavigationPopState
| NavigationLink;
```
</div>
## NavigationBase
<div class="ts-block">
```dts
interface NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
from: NavigationTarget | null;
```
<div class="ts-block-property-details">
Where navigation was triggered from
</div>
</div>
<div class="ts-block-property">
```dts
to: NavigationTarget | null;
```
<div class="ts-block-property-details">
Where navigation is going to/has gone to
</div>
</div>
<div class="ts-block-property">
```dts
willUnload: boolean;
```
<div class="ts-block-property-details">
Whether or not the navigation will result in the page being unloaded (i.e. not a client-side navigation).
</div>
</div>
<div class="ts-block-property">
```dts
complete: Promise<void>;
```
<div class="ts-block-property-details">
A promise that resolves once the navigation is complete, and rejects if the navigation
fails or is aborted. In the case of a `willUnload` navigation, the promise will never resolve
</div>
</div></div>
## NavigationEnter
<div class="ts-block">
```dts
interface NavigationEnter extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'enter';
```
<div class="ts-block-property-details">
The type of navigation:
- `enter`: The app has hydrated/started
</div>
</div>
<div class="ts-block-property">
```dts
delta?: undefined;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div>
<div class="ts-block-property">
```dts
event?: undefined;
```
<div class="ts-block-property-details">
Dispatched `Event` object when navigation occurred by `popstate` or `link`.
</div>
</div></div>
## NavigationEvent
<div class="ts-block">
```dts
interface NavigationEvent<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
RouteId extends AppRouteId | null = AppRouteId | null
> {/*…*/}
```
<div class="ts-block-property">
```dts
params: Params;
```
<div class="ts-block-property-details">
The parameters of the current page - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object
</div>
</div>
<div class="ts-block-property">
```dts
route: {/*…*/}
```
<div class="ts-block-property-details">
Info about the current route
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
id: RouteId;
```
<div class="ts-block-property-details">
The ID of the current route - e.g. for `src/routes/blog/[slug]`, it would be `/blog/[slug]`. It is `null` when no route is matched.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
url: URL;
```
<div class="ts-block-property-details">
The URL of the current page
</div>
</div></div>
## NavigationExternal
<div class="ts-block">
```dts
type NavigationExternal = NavigationGoto | NavigationLeave;
```
</div>
## NavigationFormSubmit
<div class="ts-block">
```dts
interface NavigationFormSubmit extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'form';
```
<div class="ts-block-property-details">
The type of navigation:
- `form`: The user submitted a `<form method="GET">`
</div>
</div>
<div class="ts-block-property">
```dts
event: SubmitEvent;
```
<div class="ts-block-property-details">
The `SubmitEvent` that caused the navigation
</div>
</div>
<div class="ts-block-property">
```dts
delta?: undefined;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div></div>
## NavigationGoto
<div class="ts-block">
```dts
interface NavigationGoto extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'goto';
```
<div class="ts-block-property-details">
The type of navigation:
- `goto`: Navigation was triggered by a `goto(...)` call or a redirect
</div>
</div>
<div class="ts-block-property">
```dts
delta?: undefined;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div></div>
## NavigationLeave
<div class="ts-block">
```dts
interface NavigationLeave extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'leave';
```
<div class="ts-block-property-details">
The type of navigation:
- `leave`: The app is being left either because the tab is being closed or a navigation to a different document is occurring
</div>
</div>
<div class="ts-block-property">
```dts
delta?: undefined;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div></div>
## NavigationLink
<div class="ts-block">
```dts
interface NavigationLink extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'link';
```
<div class="ts-block-property-details">
The type of navigation:
- `link`: Navigation was triggered by a link click
</div>
</div>
<div class="ts-block-property">
```dts
event: PointerEvent;
```
<div class="ts-block-property-details">
The `PointerEvent` that caused the navigation
</div>
</div>
<div class="ts-block-property">
```dts
delta?: undefined;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div></div>
## NavigationPopState
<div class="ts-block">
```dts
interface NavigationPopState extends NavigationBase {/*…*/}
```
<div class="ts-block-property">
```dts
type: 'popstate';
```
<div class="ts-block-property-details">
The type of navigation:
- `popstate`: Navigation was triggered by back/forward navigation
</div>
</div>
<div class="ts-block-property">
```dts
delta: number;
```
<div class="ts-block-property-details">
In case of a history back/forward navigation, the number of steps to go back/forward
</div>
</div>
<div class="ts-block-property">
```dts
event: PopStateEvent;
```
<div class="ts-block-property-details">
The `PopStateEvent` that caused the navigation
</div>
</div></div>
## NavigationTarget
Information about the target of a specific navigation.
<div class="ts-block">
```dts
interface NavigationTarget<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
RouteId extends AppRouteId | null = AppRouteId | null
> {/*…*/}
```
<div class="ts-block-property">
```dts
params: Params | null;
```
<div class="ts-block-property-details">
Parameters of the target page - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object.
Is `null` if the target is not part of the SvelteKit app (could not be resolved to a route).
</div>
</div>
<div class="ts-block-property">
```dts
route: {/*…*/}
```
<div class="ts-block-property-details">
Info about the target route
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
id: RouteId | null;
```
<div class="ts-block-property-details">
The ID of the current route - e.g. for `src/routes/blog/[slug]`, it would be `/blog/[slug]`. It is `null` when no route is matched.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
url: URL;
```
<div class="ts-block-property-details">
The URL that is navigated to
</div>
</div>
<div class="ts-block-property">
```dts
scroll: { x: number; y: number } | null;
```
<div class="ts-block-property-details">
The scroll position associated with this navigation.
For the `from` target, this is the scroll position at the moment of navigation.
For the `to` target, this represents the scroll position that will be or was restored:
- In `beforeNavigate` and `onNavigate`, this is only available for `popstate` navigations (back/forward button)
and will be `null` for other navigation types, since the final scroll position isn't known
ahead of time.
- In `afterNavigate`, this is always the scroll position that was applied after the navigation
completed.
</div>
</div></div>
## NavigationType
- `enter`: The app has hydrated/started
- `form`: The user submitted a `<form method="GET">`
- `leave`: The app is being left either because the tab is being closed or a navigation to a different document is occurring
- `link`: Navigation was triggered by a link click
- `goto`: Navigation was triggered by a `goto(...)` call or a redirect
- `popstate`: Navigation was triggered by back/forward navigation
<div class="ts-block">
```dts
type NavigationType =
| 'enter'
| 'form'
| 'leave'
| 'link'
| 'goto'
| 'popstate';
```
</div>
## NumericRange
<div class="ts-block">
```dts
type NumericRange<
TStart extends number,
TEnd extends number
> = Exclude<TEnd | LessThan<TEnd>, LessThan<TStart>>;
```
</div>
## OnNavigate
The argument passed to [`onNavigate`](/docs/kit/$app-navigation#onNavigate) callbacks.
<div class="ts-block">
```dts
type OnNavigate = Navigation & {
type: Exclude<NavigationType, 'enter' | 'leave'>;
/**
* Since `onNavigate` callbacks are called immediately before a client-side navigation, they will never be called with a navigation that unloads the page.
*/
willUnload: false;
};
```
</div>
## Page
The shape of the [`page`](/docs/kit/$app-state#page) reactive object and the [`$page`](/docs/kit/$app-stores) store.
<div class="ts-block">
```dts
interface Page<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
RouteId extends AppRouteId | null = AppRouteId | null
> {/*…*/}
```
<div class="ts-block-property">
```dts
url: URL & { pathname: ResolvedPathname };
```
<div class="ts-block-property-details">
The URL of the current page.
</div>
</div>
<div class="ts-block-property">
```dts
params: Params;
```
<div class="ts-block-property-details">
The parameters of the current page - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object.
</div>
</div>
<div class="ts-block-property">
```dts
route: {/*…*/}
```
<div class="ts-block-property-details">
Info about the current route.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
id: RouteId;
```
<div class="ts-block-property-details">
The ID of the current route - e.g. for `src/routes/blog/[slug]`, it would be `/blog/[slug]`. It is `null` when no route is matched.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
status: number;
```
<div class="ts-block-property-details">
HTTP status code of the current page.
</div>
</div>
<div class="ts-block-property">
```dts
error: App.Error | null;
```
<div class="ts-block-property-details">
The error object of the current page, if any. Filled from the `handleError` hooks.
</div>
</div>
<div class="ts-block-property">
```dts
data: App.PageData & Record<string, any>;
```
<div class="ts-block-property-details">
The merged result of all data from all `load` functions on the current page. You can type a common denominator through `App.PageData`.
</div>
</div>
<div class="ts-block-property">
```dts
state: App.PageState;
```
<div class="ts-block-property-details">
The page state, which can be manipulated using the [`pushState`](/docs/kit/$app-navigation#pushState) and [`replaceState`](/docs/kit/$app-navigation#replaceState) functions from `$app/navigation`.
</div>
</div>
<div class="ts-block-property">
```dts
form: any;
```
<div class="ts-block-property-details">
Filled only after a form submission. See [form actions](/docs/kit/form-actions) for more info.
</div>
</div></div>
## ParamMatcher
The shape of a param matcher. See [matching](/docs/kit/advanced-routing#Matching) for more info.
<div class="ts-block">
```dts
type ParamMatcher = (param: string) => boolean;
```
</div>
## PrerenderOption
<div class="ts-block">
```dts
type PrerenderOption = boolean | 'auto';
```
</div>
## QueryRequestedResult
<div class="ts-block">
```dts
type QueryRequestedResult<Validated, Output> = Iterable<
RequestedEntry<Validated, Output>
> &
AsyncIterable<RequestedEntry<Validated, Output>> & {
/**
* Call `refresh` on all queries selected by this `requested` invocation.
* This is identical to:
* ```ts
* import { requested } from '$app/server';
*
* for await (const { query } of requested(getPost, ...)) {
* void query.refresh();
* }
* ```
*/
refreshAll: () => Promise<void>;
};
```
</div>
## Redirect
The object returned by the [`redirect`](/docs/kit/@sveltejs-kit#redirect) function.
<div class="ts-block">
```dts
interface Redirect {/*…*/}
```
<div class="ts-block-property">
```dts
status: 300 | 301 | 302 | 303 | 304 | 305 | 306 | 307 | 308;
```
<div class="ts-block-property-details">
The [HTTP status code](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status#redirection_messages), in the range 300-308.
</div>
</div>
<div class="ts-block-property">
```dts
location: string;
```
<div class="ts-block-property-details">
The location to redirect to.
</div>
</div></div>
## RemoteCommand
The type of a remote `command` function. See [Remote functions](/docs/kit/remote-functions#command) for full documentation.
<div class="ts-block">
```dts
type RemoteCommand<Input, Output> = {
(
arg: undefined extends Input ? Input | void : Input
): Promise<Output> & {
updates(
...updates: RemoteQueryUpdate[]
): Promise<Output>;
};
/** The number of pending command executions */
get pending(): number;
};
```
</div>
## RemoteForm
The type of a remote `form` function. See [Remote functions](/docs/kit/remote-functions#form) for full documentation.
<div class="ts-block">
```dts
type RemoteForm<
Input extends RemoteFormInput | void,
Output
> = {
/** Attachment that sets up an event handler that intercepts the form submission on the client to prevent a full page reload */
[attachment: symbol]: (node: HTMLFormElement) => void;
method: 'POST';
/** The URL to send the form to. */
action: string;
/** Use the `enhance` method to influence what happens when the form is submitted. */
enhance(
callback: (opts: {
form: HTMLFormElement;
data: Input;
submit: () => Promise<boolean> & {
updates: (
...updates: RemoteQueryUpdate[]
) => Promise<boolean>;
};
}) => MaybePromise<void>
): {
method: 'POST';
action: string;
[attachment: symbol]: (node: HTMLFormElement) => void;
};
/**
* Create an instance of the form for the given `id`.
* The `id` is stringified and used for deduplication to potentially reuse existing instances.
* Useful when you have multiple forms that use the same remote form action, for example in a loop.
* ```svelte
* {#each todos as todo}
* {@const todoForm = updateTodo.for(todo.id)}
* <form {...todoForm}>
* {#if todoForm.result?.invalid}<p>Invalid data</p>{/if}
* ...
* </form>
* {/each}
* ```
*/
for(
id: ExtractId<Input>
): Omit<RemoteForm<Input, Output>, 'for'>;
/** Preflight checks */
preflight(
schema: StandardSchemaV1<Input, any>
): RemoteForm<Input, Output>;
/** Validate the form contents programmatically */
validate(options?: {
/** Set this to `true` to also show validation issues of fields that haven't been touched yet. */
includeUntouched?: boolean;
/** Set this to `true` to only run the `preflight` validation. */
preflightOnly?: boolean;
}): Promise<void>;
/** The result of the form submission */
get result(): Output | undefined;
/** The number of pending submissions */
get pending(): number;
/** Access form fields using object notation */
fields: RemoteFormFieldsRoot<Input>;
};
```
</div>
## RemoteFormField
Form field accessor type that provides name(), value(), and issues() methods
<div class="ts-block">
```dts
type RemoteFormField<Value extends RemoteFormFieldValue> =
RemoteFormFieldMethods<Value> & {
/**
* Returns an object that can be spread onto an input element with the correct type attribute,
* aria-invalid attribute if the field is invalid, and appropriate value/checked property getters/setters.
* @example
* ```svelte
* <input {...myForm.fields.myString.as('text')} />
* <input {...myForm.fields.myNumber.as('number')} />
* <input {...myForm.fields.myBoolean.as('checkbox')} />
* ```
*/
as<T extends RemoteFormFieldType<Value>>(
...args: AsArgs<T, Value>
): InputElementProps<T>;
};
```
</div>
## RemoteFormFieldType
<div class="ts-block">
```dts
type RemoteFormFieldType<T> = {
[K in keyof InputTypeMap]: T extends InputTypeMap[K]
? K
: never;
}[keyof InputTypeMap];
```
</div>
## RemoteFormFieldValue
<div class="ts-block">
```dts
type RemoteFormFieldValue =
| string
| string[]
| number
| boolean
| File
| File[];
```
</div>
## RemoteFormFields
Recursive type to build form fields structure with proxy access
<div class="ts-block">
```dts
type RemoteFormFields<T> =
WillRecurseIndefinitely<T> extends true
? RecursiveFormFields
: NonNullable<T> extends
| string
| number
| boolean
| File
? RemoteFormField<NonNullable<T>>
: // [NonNullable<T>] is used to prevent distributing over union while still allowing
// nullable wrappers (e.g. `string[] | undefined` from a schema with `.default([])`)
// to be treated as arrays; only the last condition should distribute over unions
[NonNullable<T>] extends [string[] | File[]]
? RemoteFormField<NonNullable<T>> & {
[K in number]: RemoteFormField<
NonNullable<T>[number]
>;
}
: [NonNullable<T>] extends [Array<infer U>]
? RemoteFormFieldContainer<NonNullable<T>> & {
[K in number]: RemoteFormFields<U>;
}
: RemoteFormFieldContainer<T> & {
[K in KeysOfUnion<T>]-?: RemoteFormFields<
ValueOfUnionKey<T, K>
>;
};
```
</div>
## RemoteFormInput
<div class="ts-block">
```dts
interface RemoteFormInput {/*…*/}
```
<div class="ts-block-property">
```dts
[key: string]: MaybeArray<string | number | boolean | File | RemoteFormInput>;
```
<div class="ts-block-property-details"></div>
</div></div>
## RemoteFormIssue
<div class="ts-block">
```dts
interface RemoteFormIssue {/*…*/}
```
<div class="ts-block-property">
```dts
message: string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
path: Array<string | number>;
```
<div class="ts-block-property-details"></div>
</div></div>
## RemoteLiveQuery
<div class="ts-block">
```dts
type RemoteLiveQuery<T> = RemoteResource<T> & {
/**
* Returns an async iterator with live updates.
* Unlike awaiting the resource directly, this can only be used _outside_ render
* (i.e. in load functions, event handlers and so on)
*/
run(): AsyncGenerator<T>;
/** `true` if the live stream is currently connected. */
readonly connected: boolean;
/** `true` once the current live stream iterator is done. */
readonly done: boolean;
/** Reconnects the live stream immediately. */
reconnect(): Promise<void>;
};
```
</div>
## RemoteLiveQueryFunction
The type of a remote `query.live` function. See [Remote functions](/docs/kit/remote-functions#query.live) for full documentation.
The optional `Validated` generic parameter represents the argument type *after* the
query's schema has validated and (optionally) transformed it, and matches the type
yielded by [`requested`](/docs/kit/$app-server#requested).
<div class="ts-block">
```dts
type RemoteLiveQueryFunction<
Input,
Output,
_Validated = Input
> = (
arg: undefined extends Input ? Input | void : Input
) => RemoteLiveQuery<Output>;
```
</div>
## RemotePrerenderFunction
The type of a remote `prerender` function. See [Remote functions](/docs/kit/remote-functions#prerender) for full documentation.
<div class="ts-block">
```dts
type RemotePrerenderFunction<Input, Output> = (
arg: undefined extends Input ? Input | void : Input
) => RemoteResource<Output>;
```
</div>
## RemoteQuery
<div class="ts-block">
```dts
type RemoteQuery<T> = RemoteResource<T> & {
/**
* Returns a plain promise with the result.
* Unlike awaiting the resource directly, this can only be used _outside_ render
* (i.e. in load functions, event handlers and so on)
*/
run(): Promise<T>;
/**
* On the client, this function will update the value of the query without re-fetching it.
*
* On the server, this can be called in the context of a `command` or `form` and the specified data will accompany the action response back to the client.
* This prevents SvelteKit needing to refresh all queries on the page in a second server round-trip.
*/
set(value: T): void;
/**
* On the client, this function will re-fetch the query from the server.
*
* On the server, this can be called in the context of a `command` or `form` and the refreshed data will accompany the action response back to the client.
* This prevents SvelteKit needing to refresh all queries on the page in a second server round-trip.
*/
refresh(): Promise<void>;
/**
* Temporarily override a query's value during a [single-flight mutation](https://svelte.dev/docs/kit/remote-functions#Single-flight-mutations) to provide optimistic updates.
*
* ```svelte
* <script>
* import { getTodos, addTodo } from './todos.remote.js';
* const todos = getTodos();
* </script>
*
* <form {...addTodo.enhance(async ({ data, submit }) => {
* await submit().updates(
* todos.withOverride((todos) => [...todos, { text: data.get('text') }])
* );
* })}>
* <input type="text" name="text" />
* <button type="submit">Add Todo</button>
* </form>
* ```
*/
withOverride(
update: (current: T) => T
): RemoteQueryOverride;
};
```
</div>
## RemoteQueryFunction
The return value of a remote `query` function. See [Remote functions](/docs/kit/remote-functions#query) for full documentation.
The optional `Validated` generic parameter represents the argument type *after* the
query's schema has validated and (optionally) transformed it — this is the type the
query's implementation function receives on the server, and the type yielded by
[`requested`](/docs/kit/$app-server#requested). For queries declared
with [Standard Schema](https://standardschema.dev/) it differs from `Input` when the
schema contains a transform (e.g. `v.pipe(v.number(), v.transform(String))` has
`Input = number` but `Validated = string`). For `'unchecked'` validators and queries
without arguments it defaults to `Input`.
<div class="ts-block">
```dts
type RemoteQueryFunction<
Input,
Output,
_Validated = Input
> = (
arg: undefined extends Input ? Input | void : Input
) => RemoteQuery<Output>;
```
</div>
## RemoteQueryOverride
<div class="ts-block">
```dts
type RemoteQueryOverride = () => void;
```
</div>
## RemoteQueryUpdate
<div class="ts-block">
```dts
type RemoteQueryUpdate =
| RemoteQuery<any>
| RemoteLiveQuery<any>
| RemoteQueryFunction<any, any>
| RemoteLiveQueryFunction<any, any>
| RemoteQueryOverride;
```
</div>
## RemoteResource
<div class="ts-block">
```dts
type RemoteResource<T> = Promise<T> & {
/** The error in case the query fails. Most often this is a [`HttpError`](https://svelte.dev/docs/kit/@sveltejs-kit#HttpError) but it isn't guaranteed to be. */
get error(): any;
/** `true` before the first result is available and during refreshes */
get loading(): boolean;
} & (
| {
/** The current value of the query. Undefined until `ready` is `true` */
get current(): undefined;
ready: false;
}
| {
/** The current value of the query. Undefined until `ready` is `true` */
get current(): T;
ready: true;
}
);
```
</div>
## RequestEvent
<div class="ts-block">
```dts
interface RequestEvent<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
RouteId extends AppRouteId | null = AppRouteId | null
> {/*…*/}
```
<div class="ts-block-property">
```dts
cookies: Cookies;
```
<div class="ts-block-property-details">
Get or set cookies related to the current request
</div>
</div>
<div class="ts-block-property">
```dts
fetch: typeof fetch;
```
<div class="ts-block-property-details">
`fetch` is equivalent to the [native `fetch` web API](https://developer.mozilla.org/en-US/docs/Web/API/fetch), with a few additional features:
- It can be used to make credentialed requests on the server, as it inherits the `cookie` and `authorization` headers for the page request.
- It can make relative requests on the server (ordinarily, `fetch` requires a URL with an origin when used in a server context).
- Internal requests (e.g. for `+server.js` routes) go directly to the handler function when running on the server, without the overhead of an HTTP call.
- During server-side rendering, the response will be captured and inlined into the rendered HTML by hooking into the `text` and `json` methods of the `Response` object. Note that headers will _not_ be serialized, unless explicitly included via [`filterSerializedResponseHeaders`](/docs/kit/hooks#Server-hooks-handle)
- During hydration, the response will be read from the HTML, guaranteeing consistency and preventing an additional network request.
You can learn more about making credentialed requests with cookies [here](/docs/kit/load#Cookies).
</div>
</div>
<div class="ts-block-property">
```dts
getClientAddress: () => string;
```
<div class="ts-block-property-details">
The client's IP address, set by the adapter.
</div>
</div>
<div class="ts-block-property">
```dts
locals: App.Locals;
```
<div class="ts-block-property-details">
Contains custom data that was added to the request within the [`server handle hook`](/docs/kit/hooks#Server-hooks-handle).
</div>
</div>
<div class="ts-block-property">
```dts
params: Params;
```
<div class="ts-block-property-details">
The parameters of the current route - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object.
</div>
</div>
<div class="ts-block-property">
```dts
platform: Readonly<App.Platform> | undefined;
```
<div class="ts-block-property-details">
Additional data made available through the adapter.
</div>
</div>
<div class="ts-block-property">
```dts
request: Request;
```
<div class="ts-block-property-details">
The original request object.
</div>
</div>
<div class="ts-block-property">
```dts
route: {/*…*/}
```
<div class="ts-block-property-details">
Info about the current route.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
id: RouteId;
```
<div class="ts-block-property-details">
The ID of the current route - e.g. for `src/routes/blog/[slug]`, it would be `/blog/[slug]`. It is `null` when no route is matched.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
setHeaders: (headers: Record<string, string>) => void;
```
<div class="ts-block-property-details">
If you need to set headers for the response, you can do so using the this method. This is useful if you want the page to be cached, for example:
```js
// @errors: 7031
/// file: src/routes/blog/+page.js
export async function load({ fetch, setHeaders }) {
const url = `https://cms.example.com/articles.json`;
const response = await fetch(url);
setHeaders({
age: response.headers.get('age'),
'cache-control': response.headers.get('cache-control')
});
return response.json();
}
```
Setting the same header multiple times (even in separate `load` functions) is an error — you can only set a given header once.
You cannot add a `set-cookie` header with `setHeaders` — use the [`cookies`](/docs/kit/@sveltejs-kit#Cookies) API instead.
</div>
</div>
<div class="ts-block-property">
```dts
url: URL;
```
<div class="ts-block-property-details">
The requested URL.
</div>
</div>
<div class="ts-block-property">
```dts
isDataRequest: boolean;
```
<div class="ts-block-property-details">
`true` if the request comes from the client asking for `+page/layout.server.js` data. The `url` property will be stripped of the internal information
related to the data request in this case. Use this property instead if the distinction is important to you.
</div>
</div>
<div class="ts-block-property">
```dts
isSubRequest: boolean;
```
<div class="ts-block-property-details">
`true` for `+server.js` calls coming from SvelteKit without the overhead of actually making an HTTP request. This happens when you make same-origin `fetch` requests on the server.
</div>
</div>
<div class="ts-block-property">
```dts
tracing: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag since">available since</span> v2.31.0
</div>
Access to spans for tracing. If tracing is not enabled, these spans will do nothing.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
enabled: boolean;
```
<div class="ts-block-property-details">
Whether tracing is enabled.
</div>
</div>
<div class="ts-block-property">
```dts
root: Span;
```
<div class="ts-block-property-details">
The root span for the request. This span is named `sveltekit.handle.root`.
</div>
</div>
<div class="ts-block-property">
```dts
current: Span;
```
<div class="ts-block-property-details">
The span associated with the current `handle` hook, `load` function, or form action.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```dts
isRemoteRequest: boolean;
```
<div class="ts-block-property-details">
`true` if the request comes from the client via a remote function. The `url` property will be stripped of the internal information
related to the data request in this case. Use this property instead if the distinction is important to you.
</div>
</div></div>
## RequestHandler
A `(event: RequestEvent) => Response` function exported from a `+server.js` file that corresponds to an HTTP verb (`GET`, `PUT`, `PATCH`, etc) and handles requests with that method.
It receives `Params` as the first generic argument, which you can skip by using [generated types](/docs/kit/types#Generated-types) instead.
<div class="ts-block">
```dts
type RequestHandler<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
RouteId extends AppRouteId | null = AppRouteId | null
> = (
event: RequestEvent<Params, RouteId>
) => MaybePromise<Response>;
```
</div>
## RequestedEntry
A single entry yielded by [`requested`](/docs/kit/$app-server#requested)
when called with a regular `query`. `arg` is the validated argument (the input *after*
the query's schema validated and transformed it, if applicable); `query` is a
`RemoteQuery` bound to the client's original cache key, so `refresh()` / `set()` will
update the correct client entry.
<div class="ts-block">
```dts
type RequestedEntry<Validated, Output> = {
arg: Validated;
query: RemoteQuery<Output>;
};
```
</div>
## RequestedResult
<div class="ts-block">
```dts
type RequestedResult<Validated, Output> =
| QueryRequestedResult<Validated, Output>
| LiveQueryRequestedResult<Validated, Output>;
```
</div>
## Reroute
<blockquote class="since note">
Available since 2.3.0
</blockquote>
The [`reroute`](/docs/kit/hooks#Universal-hooks-reroute) hook allows you to modify the URL before it is used to determine which route to render.
<div class="ts-block">
```dts
type Reroute = (event: {
url: URL;
fetch: typeof fetch;
}) => MaybePromise<void | string>;
```
</div>
## ResolveOptions
<div class="ts-block">
```dts
interface ResolveOptions {/*…*/}
```
<div class="ts-block-property">
```dts
transformPageChunk?: (input: { html: string; done: boolean }) => MaybePromise<string | undefined>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `input` the html chunk and the info if this is the last chunk
</div>
Applies custom transforms to HTML. If `done` is true, it's the final chunk. Chunks are not guaranteed to be well-formed HTML
(they could include an element's opening tag but not its closing tag, for example)
but they will always be split at sensible boundaries such as `%sveltekit.head%` or layout/page components.
</div>
</div>
<div class="ts-block-property">
```dts
filterSerializedResponseHeaders?: (name: string, value: string) => boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `name` header name
- `value` header value
</div>
Determines which headers should be included in serialized responses when a `load` function loads a resource with `fetch`.
By default, none will be included.
</div>
</div>
<div class="ts-block-property">
```dts
preload?: (input: { type: 'font' | 'css' | 'js' | 'asset'; path: string }) => boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- `input` the type of the file and its path
</div>
Determines what should be added to the `<head>` tag to preload it.
By default, `js` and `css` files will be preloaded.
</div>
</div></div>
## RouteDefinition
<div class="ts-block">
```dts
interface RouteDefinition<Config = any> {/*…*/}
```
<div class="ts-block-property">
```dts
id: string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
api: {
methods: Array<HttpMethod | '*'>;
};
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
page: {
methods: Array<Extract<HttpMethod, 'GET' | 'POST'>>;
};
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
pattern: RegExp;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
prerender: PrerenderOption;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
segments: RouteSegment[];
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
methods: Array<HttpMethod | '*'>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
config: Config;
```
<div class="ts-block-property-details"></div>
</div></div>
## SSRManifest
<div class="ts-block">
```dts
interface SSRManifest {/*…*/}
```
<div class="ts-block-property">
```dts
appDir: string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
appPath: string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
assets: Set<string>;
```
<div class="ts-block-property-details">
Static files from `kit.config.files.assets` and the service worker (if any).
</div>
</div>
<div class="ts-block-property">
```dts
mimeTypes: Record<string, string>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
_: {/*…*/}
```
<div class="ts-block-property-details">
private fields
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
client: NonNullable<BuildData['client']>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
nodes: SSRNodeLoader[];
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
remotes: Record<string, () => Promise<any>>;
```
<div class="ts-block-property-details">
hashed filename -> import to that file
</div>
</div>
<div class="ts-block-property">
```dts
routes: SSRRoute[];
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
prerendered_routes: Set<string>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
matchers: () => Promise<Record<string, ParamMatcher>>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
server_assets: Record<string, number>;
```
<div class="ts-block-property-details">
A `[file]: size` map of all assets imported by server code.
</div>
</div></div>
</div>
</div></div>
## ServerInit
<blockquote class="since note">
Available since 2.10.0
</blockquote>
The [`init`](/docs/kit/hooks#Shared-hooks-init) will be invoked before the server responds to its first request
<div class="ts-block">
```dts
type ServerInit = () => MaybePromise<void>;
```
</div>
## ServerInitOptions
<div class="ts-block">
```dts
interface ServerInitOptions {/*…*/}
```
<div class="ts-block-property">
```dts
env: Record<string, string>;
```
<div class="ts-block-property-details">
A map of environment variables.
</div>
</div>
<div class="ts-block-property">
```dts
read?: (file: string) => MaybePromise<ReadableStream | null>;
```
<div class="ts-block-property-details">
A function that turns an asset filename into a `ReadableStream`. Required for the `read` export from `$app/server` to work.
</div>
</div></div>
## ServerLoad
The generic form of `PageServerLoad` and `LayoutServerLoad`. You should import those from `./$types` (see [generated types](/docs/kit/types#Generated-types))
rather than using `ServerLoad` directly.
<div class="ts-block">
```dts
type ServerLoad<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
ParentData extends Record<string, any> = Record<
string,
any
>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends AppRouteId | null = AppRouteId | null
> = (
event: ServerLoadEvent<Params, ParentData, RouteId>
) => MaybePromise<OutputData>;
```
</div>
## ServerLoadEvent
<div class="ts-block">
```dts
interface ServerLoadEvent<
Params extends AppLayoutParams<'/'> =
AppLayoutParams<'/'>,
ParentData extends Record<string, any> = Record<
string,
any
>,
RouteId extends AppRouteId | null = AppRouteId | null
> extends RequestEvent<Params, RouteId> {/*…*/}
```
<div class="ts-block-property">
```dts
parent: () => Promise<ParentData>;
```
<div class="ts-block-property-details">
`await parent()` returns data from parent `+layout.server.js` `load` functions.
Be careful not to introduce accidental waterfalls when using `await parent()`. If for example you only want to merge parent data into the returned output, call it _after_ fetching your other data.
</div>
</div>
<div class="ts-block-property">
```dts
depends: (...deps: string[]) => void;
```
<div class="ts-block-property-details">
This function declares that the `load` function has a _dependency_ on one or more URLs or custom identifiers, which can subsequently be used with [`invalidate()`](/docs/kit/$app-navigation#invalidate) to cause `load` to rerun.
Most of the time you won't need this, as `fetch` calls `depends` on your behalf — it's only necessary if you're using a custom API client that bypasses `fetch`.
URLs can be absolute or relative to the page being loaded, and must be [encoded](https://developer.mozilla.org/en-US/docs/Glossary/percent-encoding).
Custom identifiers have to be prefixed with one or more lowercase letters followed by a colon to conform to the [URI specification](https://www.rfc-editor.org/rfc/rfc3986.html).
The following example shows how to use `depends` to register a dependency on a custom identifier, which is `invalidate`d after a button click, making the `load` function rerun.
```js
// @errors: 7031
/// file: src/routes/+page.js
let count = 0;
export async function load({ depends }) {
depends('increase:count');
return { count: count++ };
}
```
```html
/// file: src/routes/+page.svelte
<script>
import { invalidate } from '$app/navigation';
let { data } = $props();
const increase = async () => {
await invalidate('increase:count');
}
</script>
<p>{data.count}<p>
<button on:click={increase}>Increase Count</button>
```
</div>
</div>
<div class="ts-block-property">
```dts
untrack: <T>(fn: () => T) => T;
```
<div class="ts-block-property-details">
Use this function to opt out of dependency tracking for everything that is synchronously called within the callback. Example:
```js
// @errors: 7031
/// file: src/routes/+page.js
export async function load({ untrack, url }) {
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}
```
</div>
</div>
<div class="ts-block-property">
```dts
tracing: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag since">available since</span> v2.31.0
</div>
Access to spans for tracing. If tracing is not enabled, these spans will do nothing.
<div class="ts-block-property-children"><div class="ts-block-property">
```dts
enabled: boolean;
```
<div class="ts-block-property-details">
Whether tracing is enabled.
</div>
</div>
<div class="ts-block-property">
```dts
root: Span;
```
<div class="ts-block-property-details">
The root span for the request. This span is named `sveltekit.handle.root`.
</div>
</div>
<div class="ts-block-property">
```dts
current: Span;
```
<div class="ts-block-property-details">
The span associated with the current server `load` function.
</div>
</div></div>
</div>
</div></div>
## Snapshot
The type of `export const snapshot` exported from a page or layout component.
<div class="ts-block">
```dts
interface Snapshot<T = any> {/*…*/}
```
<div class="ts-block-property">
```dts
capture: () => T;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
restore: (snapshot: T) => void;
```
<div class="ts-block-property-details"></div>
</div></div>
## SubmitFunction
<div class="ts-block">
```dts
type SubmitFunction<
Success extends Record<string, unknown> | undefined =
Record<string, any>,
Failure extends Record<string, unknown> | undefined =
Record<string, any>
> = (input: {
action: URL;
formData: FormData;
formElement: HTMLFormElement;
controller: AbortController;
submitter: HTMLElement | null;
cancel: () => void;
}) => MaybePromise<
| void
| ((opts: {
formData: FormData;
formElement: HTMLFormElement;
action: URL;
result: ActionResult<Success, Failure>;
/**
* Call this to get the default behavior of a form submission response.
* @param options Set `reset: false` if you don't want the `<form>` values to be reset after a successful submission.
* @param invalidateAll Set `invalidateAll: false` if you don't want the action to call `invalidateAll` after submission.
*/
update: (options?: {
reset?: boolean;
invalidateAll?: boolean;
}) => Promise<void>;
}) => MaybePromise<void>)
>;
```
</div>
## Transport
<blockquote class="since note">
Available since 2.11.0
</blockquote>
The [`transport`](/docs/kit/hooks#Universal-hooks-transport) hook allows you to transport custom types across the server/client boundary.
Each transporter has a pair of `encode` and `decode` functions. On the server, `encode` determines whether a value is an instance of the custom type and, if so, returns a non-falsy encoding of the value which can be an object or an array (or `false` otherwise).
In the browser, `decode` turns the encoding back into an instance of the custom type.
```ts
import type { Transport } from '@sveltejs/kit';
declare class MyCustomType {
data: any
}
// hooks.js
export const transport: Transport = {
MyCustomType: {
encode: (value) => value instanceof MyCustomType && [value.data],
decode: ([data]) => new MyCustomType(data)
}
};
```
<div class="ts-block">
```dts
type Transport = Record<string, Transporter>;
```
</div>
## Transporter
A member of the [`transport`](/docs/kit/hooks#Universal-hooks-transport) hook.
<div class="ts-block">
```dts
interface Transporter<
T = any,
U = Exclude<
any,
false | 0 | '' | null | undefined | typeof NaN
>
> {/*…*/}
```
<div class="ts-block-property">
```dts
encode: (value: T) => false | U;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
decode: (data: U) => T;
```
<div class="ts-block-property-details"></div>
</div></div>
## ValidationError
A validation error thrown by `invalid`.
<div class="ts-block">
```dts
interface ValidationError {/*…*/}
```
<div class="ts-block-property">
```dts
issues: StandardSchemaV1.Issue[];
```
<div class="ts-block-property-details">
The validation issues
</div>
</div></div>
## Private types
The following are referenced by the public types documented above, but cannot be imported directly:
## AdapterEntry
<div class="ts-block">
```dts
interface AdapterEntry {/*…*/}
```
<div class="ts-block-property">
```dts
id: string;
```
<div class="ts-block-property-details">
A string that uniquely identifies an HTTP service (e.g. serverless function) and is used for deduplication.
For example, `/foo/a-[b]` and `/foo/[c]` are different routes, but would both
be represented in a Netlify _redirects file as `/foo/:param`, so they share an ID
</div>
</div>
<div class="ts-block-property">
```dts
filter(route: RouteDefinition): boolean;
```
<div class="ts-block-property-details">
A function that compares the candidate route with the current route to determine
if it should be grouped with the current route.
Use cases:
- Fallback pages: `/foo/[c]` is a fallback for `/foo/a-[b]`, and `/[...catchall]` is a fallback for all routes
- Grouping routes that share a common `config`: `/foo` should be deployed to the edge, `/bar` and `/baz` should be deployed to a serverless function
</div>
</div>
<div class="ts-block-property">
```dts
complete(entry: { generateManifest(opts: { relativePath: string }): string }): MaybePromise<void>;
```
<div class="ts-block-property-details">
A function that is invoked once the entry has been created. This is where you
should write the function to the filesystem and generate redirect manifests.
</div>
</div></div>
## Csp
<div class="ts-block">
```dts
namespace Csp {
type ActionSource = 'strict-dynamic' | 'report-sample';
type BaseSource =
| 'self'
| 'unsafe-eval'
| 'unsafe-hashes'
| 'unsafe-inline'
| 'wasm-unsafe-eval'
| 'none';
type CryptoSource =
`${'nonce' | 'sha256' | 'sha384' | 'sha512'}-${string}`;
type FrameSource =
| HostSource
| SchemeSource
| 'self'
| 'none';
type HostNameScheme = `${string}.${string}` | 'localhost';
type HostSource =
`${HostProtocolSchemes}${HostNameScheme}${PortScheme}`;
type HostProtocolSchemes = `${string}://` | '';
type HttpDelineator = '/' | '?' | '#' | '\\';
type PortScheme = `:${number}` | '' | ':*';
type SchemeSource =
| 'http:'
| 'https:'
| 'data:'
| 'mediastream:'
| 'blob:'
| 'filesystem:';
type Source =
| HostSource
| SchemeSource
| CryptoSource
| BaseSource;
type Sources = Source[];
}
```
</div>
## CspDirectives
<div class="ts-block">
```dts
interface CspDirectives {/*…*/}
```
<div class="ts-block-property">
```dts
'child-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'default-src'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'frame-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'worker-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'connect-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'font-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'img-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'manifest-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'media-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'object-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'prefetch-src'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'script-src'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'script-src-elem'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'script-src-attr'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'style-src'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'style-src-elem'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'style-src-attr'?: Csp.Sources;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'base-uri'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
sandbox?: Array<
| 'allow-downloads-without-user-activation'
| 'allow-forms'
| 'allow-modals'
| 'allow-orientation-lock'
| 'allow-pointer-lock'
| 'allow-popups'
| 'allow-popups-to-escape-sandbox'
| 'allow-presentation'
| 'allow-same-origin'
| 'allow-scripts'
| 'allow-storage-access-by-user-activation'
| 'allow-top-navigation'
| 'allow-top-navigation-by-user-activation'
>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'form-action'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'frame-ancestors'?: Array<Csp.HostSource | Csp.SchemeSource | Csp.FrameSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'navigate-to'?: Array<Csp.Source | Csp.ActionSource>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'report-uri'?: string[];
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'report-to'?: string[];
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'require-trusted-types-for'?: Array<'script'>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'trusted-types'?: Array<'none' | 'allow-duplicates' | '*' | string>;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'upgrade-insecure-requests'?: boolean;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
'require-sri-for'?: Array<'script' | 'style' | 'script style'>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span>
</div>
</div>
</div>
<div class="ts-block-property">
```dts
'block-all-mixed-content'?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span>
</div>
</div>
</div>
<div class="ts-block-property">
```dts
'plugin-types'?: Array<`${string}/${string}` | 'none'>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span>
</div>
</div>
</div>
<div class="ts-block-property">
```dts
referrer?: Array<
| 'no-referrer'
| 'no-referrer-when-downgrade'
| 'origin'
| 'origin-when-cross-origin'
| 'same-origin'
| 'strict-origin'
| 'strict-origin-when-cross-origin'
| 'unsafe-url'
| 'none'
>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span>
</div>
</div>
</div></div>
## DeepPartial
<div class="ts-block">
```dts
type DeepPartial<T> = T extends
| Record<PropertyKey, unknown>
| unknown[]
? {
[K in keyof T]?: T[K] extends
| Record<PropertyKey, unknown>
| unknown[]
? DeepPartial<T[K]>
: T[K];
}
: T | undefined;
```
</div>
## HttpMethod
<div class="ts-block">
```dts
type HttpMethod =
| 'GET'
| 'HEAD'
| 'POST'
| 'PUT'
| 'DELETE'
| 'PATCH'
| 'OPTIONS';
```
</div>
## IsAny
<div class="ts-block">
```dts
type IsAny<T> = 0 extends 1 & T ? true : false;
```
</div>
## Logger
<div class="ts-block">
```dts
interface Logger {/*…*/}
```
<div class="ts-block-property">
```dts
(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
success(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
error(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
warn(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
minor(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
info(msg: string): void;
```
<div class="ts-block-property-details"></div>
</div></div>
## MaybePromise
<div class="ts-block">
```dts
type MaybePromise<T> = T | Promise<T>;
```
</div>
## PrerenderEntryGeneratorMismatchHandler
<div class="ts-block">
```dts
interface PrerenderEntryGeneratorMismatchHandler {/*…*/}
```
<div class="ts-block-property">
```dts
(details: { generatedFromId: string; entry: string; matchedId: string; message: string }): void;
```
<div class="ts-block-property-details"></div>
</div></div>
## PrerenderEntryGeneratorMismatchHandlerValue
<div class="ts-block">
```dts
type PrerenderEntryGeneratorMismatchHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderEntryGeneratorMismatchHandler;
```
</div>
## PrerenderHttpErrorHandler
<div class="ts-block">
```dts
interface PrerenderHttpErrorHandler {/*…*/}
```
<div class="ts-block-property">
```dts
(details: {
status: number;
path: string;
referrer: string | null;
referenceType: 'linked' | 'fetched';
message: string;
}): void;
```
<div class="ts-block-property-details"></div>
</div></div>
## PrerenderHttpErrorHandlerValue
<div class="ts-block">
```dts
type PrerenderHttpErrorHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderHttpErrorHandler;
```
</div>
## PrerenderMap
<div class="ts-block">
```dts
type PrerenderMap = Map<string, PrerenderOption>;
```
</div>
## PrerenderMissingIdHandler
<div class="ts-block">
```dts
interface PrerenderMissingIdHandler {/*…*/}
```
<div class="ts-block-property">
```dts
(details: { path: string; id: string; referrers: string[]; message: string }): void;
```
<div class="ts-block-property-details"></div>
</div></div>
## PrerenderMissingIdHandlerValue
<div class="ts-block">
```dts
type PrerenderMissingIdHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderMissingIdHandler;
```
</div>
## PrerenderOption
<div class="ts-block">
```dts
type PrerenderOption = boolean | 'auto';
```
</div>
## PrerenderUnseenRoutesHandler
<div class="ts-block">
```dts
interface PrerenderUnseenRoutesHandler {/*…*/}
```
<div class="ts-block-property">
```dts
(details: { routes: string[]; message: string }): void;
```
<div class="ts-block-property-details"></div>
</div></div>
## PrerenderUnseenRoutesHandlerValue
<div class="ts-block">
```dts
type PrerenderUnseenRoutesHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderUnseenRoutesHandler;
```
</div>
## Prerendered
<div class="ts-block">
```dts
interface Prerendered {/*…*/}
```
<div class="ts-block-property">
```dts
pages: Map<
string,
{
/** The location of the .html file relative to the output directory */
file: string;
}
>;
```
<div class="ts-block-property-details">
A map of `path` to `{ file }` objects, where a path like `/foo` corresponds to `foo.html` and a path like `/bar/` corresponds to `bar/index.html`.
</div>
</div>
<div class="ts-block-property">
```dts
assets: Map<
string,
{
/** The MIME type of the asset */
type: string;
}
>;
```
<div class="ts-block-property-details">
A map of `path` to `{ type }` objects.
</div>
</div>
<div class="ts-block-property">
```dts
redirects: Map<
string,
{
status: number;
location: string;
}
>;
```
<div class="ts-block-property-details">
A map of redirects encountered during prerendering.
</div>
</div>
<div class="ts-block-property">
```dts
paths: string[];
```
<div class="ts-block-property-details">
An array of prerendered paths (without trailing slashes, regardless of the trailingSlash config)
</div>
</div></div>
## RequestOptions
<div class="ts-block">
```dts
interface RequestOptions {/*…*/}
```
<div class="ts-block-property">
```dts
getClientAddress(): string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
platform?: App.Platform;
```
<div class="ts-block-property-details"></div>
</div></div>
## RouteSegment
<div class="ts-block">
```dts
interface RouteSegment {/*…*/}
```
<div class="ts-block-property">
```dts
content: string;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
dynamic: boolean;
```
<div class="ts-block-property-details"></div>
</div>
<div class="ts-block-property">
```dts
rest: boolean;
```
<div class="ts-block-property-details"></div>
</div></div>
## TrailingSlash
<div class="ts-block">
```dts
type TrailingSlash = 'never' | 'always' | 'ignore';
```
</div>
# @sveltejs/kit/hooks
```js
// @noErrors
import { sequence } from '@sveltejs/kit/hooks';
```
## sequence
A helper function for sequencing multiple `handle` calls in a middleware-like manner.
The behavior for the `handle` options is as follows:
- `transformPageChunk` is applied in reverse order and merged
- `preload` is applied in forward order, the first option "wins" and no `preload` options after it are called
- `filterSerializedResponseHeaders` behaves the same as `preload`
```js
// @errors: 7031
/// file: src/hooks.server.js
import { sequence } from '@sveltejs/kit/hooks';
/** @type {import('@sveltejs/kit').Handle} */
async function first({ event, resolve }) {
console.log('first pre-processing');
const result = await resolve(event, {
transformPageChunk: ({ html }) => {
// transforms are applied in reverse order
console.log('first transform');
return html;
},
preload: () => {
// this one wins as it's the first defined in the chain
console.log('first preload');
return true;
}
});
console.log('first post-processing');
return result;
}
/** @type {import('@sveltejs/kit').Handle} */
async function second({ event, resolve }) {
console.log('second pre-processing');
const result = await resolve(event, {
transformPageChunk: ({ html }) => {
console.log('second transform');
return html;
},
preload: () => {
console.log('second preload');
return true;
},
filterSerializedResponseHeaders: () => {
// this one wins as it's the first defined in the chain
console.log('second filterSerializedResponseHeaders');
return true;
}
});
console.log('second post-processing');
return result;
}
export const handle = sequence(first, second);
```
The example above would print:
```
first pre-processing
first preload
second pre-processing
second filterSerializedResponseHeaders
second transform
first transform
second post-processing
first post-processing
```
<div class="ts-block">
```dts
function sequence(...handlers: Handle[]): Handle;
```
</div>
# @sveltejs/kit/node/polyfills
```js
// @noErrors
import { installPolyfills } from '@sveltejs/kit/node/polyfills';
```
## installPolyfills
Make various web APIs available as globals:
- `crypto`
- `File`
<div class="ts-block">
```dts
function installPolyfills(): void;
```
</div>
# @sveltejs/kit/node
```js
// @noErrors
import {
createReadableStream,
getRequest,
setResponse
} from '@sveltejs/kit/node';
```
## createReadableStream
<blockquote class="since note">
Available since 2.4.0
</blockquote>
Converts a file on disk to a readable stream
<div class="ts-block">
```dts
function createReadableStream(file: string): ReadableStream;
```
</div>
## getRequest
<div class="ts-block">
```dts
function getRequest({
request,
base,
bodySizeLimit
}: {
request: import('http').IncomingMessage;
base: string;
bodySizeLimit?: number;
}): Promise<Request>;
```
</div>
## setResponse
<div class="ts-block">
```dts
function setResponse(
res: import('http').ServerResponse,
response: Response
): Promise<void>;
```
</div>
# @sveltejs/kit/vite
```js
// @noErrors
import { sveltekit } from '@sveltejs/kit/vite';
```
## sveltekit
Returns the SvelteKit Vite plugins.
<div class="ts-block">
```dts
function sveltekit(): Promise<Plugin[]>;
```
</div>
# $app/environment
```js
// @noErrors
import { browser, building, dev, version } from '$app/environment';
```
## browser
`true` if the app is running in the browser.
<div class="ts-block">
```dts
const browser: boolean;
```
</div>
## building
SvelteKit analyses your app during the `build` step by running it. During this process, `building` is `true`. This also applies during prerendering.
<div class="ts-block">
```dts
const building: boolean;
```
</div>
## dev
Whether the dev server is running. This is not guaranteed to correspond to `NODE_ENV` or `MODE`.
<div class="ts-block">
```dts
const dev: boolean;
```
</div>
## version
The value of `config.kit.version.name`.
<div class="ts-block">
```dts
const version: string;
```
</div>
# $app/forms
```js
// @noErrors
import { applyAction, deserialize, enhance } from '$app/forms';
```
## applyAction
This action updates the `form` property of the current page with the given data and updates `page.status`.
In case of an error, it redirects to the nearest error page.
<div class="ts-block">
```dts
function applyAction<
Success extends Record<string, unknown> | undefined,
Failure extends Record<string, unknown> | undefined
>(
result: import('@sveltejs/kit').ActionResult<
Success,
Failure
>
): Promise<void>;
```
</div>
## deserialize
Use this function to deserialize the response from a form submission.
Usage:
```js
// @errors: 7031
import { deserialize } from '$app/forms';
async function handleSubmit(event) {
const response = await fetch('/form?/action', {
method: 'POST',
body: new FormData(event.target)
});
const result = deserialize(await response.text());
// ...
}
```
<div class="ts-block">
```dts
function deserialize<
Success extends Record<string, unknown> | undefined,
Failure extends Record<string, unknown> | undefined
>(
result: string
): import('@sveltejs/kit').ActionResult<Success, Failure>;
```
</div>
## enhance
This action enhances a `<form>` element that otherwise would work without JavaScript.
The `submit` function is called upon submission with the given FormData and the `action` that should be triggered.
If `cancel` is called, the form will not be submitted.
You can use the abort `controller` to cancel the submission in case another one starts.
If a function is returned, that function is called with the response from the server.
If nothing is returned, the fallback will be used.
If this function or its return value isn't set, it
- falls back to updating the `form` prop with the returned data if the action is on the same page as the form
- updates `page.status`
- resets the `<form>` element and invalidates all data in case of successful submission with no redirect response
- redirects in case of a redirect response
- redirects to the nearest error page in case of an unexpected error
If you provide a custom function with a callback and want to use the default behavior, invoke `update` in your callback.
It accepts an options object
- `reset: false` if you don't want the `<form>` values to be reset after a successful submission
- `invalidateAll: false` if you don't want the action to call `invalidateAll` after submission
<div class="ts-block">
```dts
function enhance<
Success extends Record<string, unknown> | undefined,
Failure extends Record<string, unknown> | undefined
>(
form_element: HTMLFormElement,
submit?: import('@sveltejs/kit').SubmitFunction<
Success,
Failure
>
): {
destroy(): void;
};
```
</div>
# $app/navigation
```js
// @noErrors
import {
afterNavigate,
beforeNavigate,
disableScrollHandling,
goto,
invalidate,
invalidateAll,
onNavigate,
preloadCode,
preloadData,
pushState,
refreshAll,
replaceState
} from '$app/navigation';
```
## afterNavigate
A lifecycle function that runs the supplied `callback` when the current component mounts, and also whenever we navigate to a URL.
`afterNavigate` must be called during a component initialization. It remains active as long as the component is mounted.
<div class="ts-block">
```dts
function afterNavigate(
callback: (
navigation: import('@sveltejs/kit').AfterNavigate
) => void
): void;
```
</div>
## beforeNavigate
A navigation interceptor that triggers before we navigate to a URL, whether by clicking a link, calling `goto(...)`, or using the browser back/forward controls.
Calling `cancel()` will prevent the navigation from completing. If `navigation.type === 'leave'` — meaning the user is navigating away from the app (or closing the tab) — calling `cancel` will trigger the native browser unload confirmation dialog. In this case, the navigation may or may not be cancelled depending on the user's response.
When a navigation isn't to a SvelteKit-owned route (and therefore controlled by SvelteKit's client-side router), `navigation.to.route.id` will be `null`.
If the navigation will (if not cancelled) cause the document to unload — in other words `'leave'` navigations and `'link'` navigations where `navigation.to.route === null` — `navigation.willUnload` is `true`.
`beforeNavigate` must be called during a component initialization. It remains active as long as the component is mounted.
<div class="ts-block">
```dts
function beforeNavigate(
callback: (
navigation: import('@sveltejs/kit').BeforeNavigate
) => void
): void;
```
</div>
## disableScrollHandling
If called when the page is being updated following a navigation (in `onMount` or `afterNavigate` or an action, for example), this disables SvelteKit's built-in scroll handling.
This is generally discouraged, since it breaks user expectations.
<div class="ts-block">
```dts
function disableScrollHandling(): void;
```
</div>
## goto
Allows you to navigate programmatically to a given route, with options such as keeping the current element focused.
Returns a Promise that resolves when SvelteKit navigates (or fails to navigate, in which case the promise rejects) to the specified `url`.
For external URLs, use `window.location = url` instead of calling `goto(url)`.
<div class="ts-block">
```dts
function goto(
url: string | URL,
opts?: {
replaceState?: boolean | undefined;
noScroll?: boolean | undefined;
keepFocus?: boolean | undefined;
invalidateAll?: boolean | undefined;
invalidate?:
| (string | URL | ((url: URL) => boolean))[]
| undefined;
state?: App.PageState | undefined;
}
): Promise<void>;
```
</div>
## invalidate
Causes any `load` functions belonging to the currently active page to re-run if they depend on the `url` in question, via `fetch` or `depends`. Returns a `Promise` that resolves when the page is subsequently updated.
If the argument is given as a `string` or `URL`, it must resolve to the same URL that was passed to `fetch` or `depends` (including query parameters).
To create a custom identifier, use a string beginning with `[a-z]+:` (e.g. `custom:state`) — this is a valid URL.
The `function` argument can be used define a custom predicate. It receives the full `URL` and causes `load` to rerun if `true` is returned.
This can be useful if you want to invalidate based on a pattern instead of a exact match.
```ts
// Example: Match '/path' regardless of the query parameters
import { invalidate } from '$app/navigation';
invalidate((url) => url.pathname === '/path');
```
<div class="ts-block">
```dts
function invalidate(
resource: string | URL | ((url: URL) => boolean)
): Promise<void>;
```
</div>
## invalidateAll
Causes all `load` and `query` functions belonging to the currently active page to re-run. Returns a `Promise` that resolves when the page is subsequently updated.
<div class="ts-block">
```dts
function invalidateAll(): Promise<void>;
```
</div>
## onNavigate
A lifecycle function that runs the supplied `callback` immediately before we navigate to a new URL except during full-page navigations.
If you return a `Promise`, SvelteKit will wait for it to resolve before completing the navigation. This allows you to — for example — use `document.startViewTransition`. Avoid promises that are slow to resolve, since navigation will appear stalled to the user.
If a function (or a `Promise` that resolves to a function) is returned from the callback, it will be called once the DOM has updated.
`onNavigate` must be called during a component initialization. It remains active as long as the component is mounted.
<div class="ts-block">
```dts
function onNavigate(
callback: (
navigation: import('@sveltejs/kit').OnNavigate
) => MaybePromise<(() => void) | void>
): void;
```
</div>
## preloadCode
Programmatically imports the code for routes that haven't yet been fetched.
Typically, you might call this to speed up subsequent navigation.
You can specify routes by any matching pathname such as `/about` (to match `src/routes/about/+page.svelte`) or `/blog/*` (to match `src/routes/blog/[slug]/+page.svelte`).
Unlike `preloadData`, this won't call `load` functions.
Returns a Promise that resolves when the modules have been imported.
<div class="ts-block">
```dts
function preloadCode(pathname: string): Promise<void>;
```
</div>
## preloadData
Programmatically preloads the given page, which means
1. ensuring that the code for the page is loaded, and
2. calling the page's load function with the appropriate options.
This is the same behaviour that SvelteKit triggers when the user taps or mouses over an `<a>` element with `data-sveltekit-preload-data`.
If the next navigation is to `href`, the values returned from load will be used, making navigation instantaneous.
Returns a Promise that resolves with the result of running the new route's `load` functions once the preload is complete.
<div class="ts-block">
```dts
function preloadData(href: string): Promise<
| {
type: 'loaded';
status: number;
data: Record<string, any>;
}
| {
type: 'redirect';
location: string;
}
>;
```
</div>
## pushState
Programmatically create a new history entry with the given `page.state`. To use the current URL, you can pass `''` as the first argument. Used for [shallow routing](/docs/kit/shallow-routing).
<div class="ts-block">
```dts
function pushState(
url: string | URL,
state: App.PageState
): void;
```
</div>
## refreshAll
Causes all currently active remote functions to refresh, and all `load` functions belonging to the currently active page to re-run (unless disabled via the option argument).
Returns a `Promise` that resolves when the page is subsequently updated.
<div class="ts-block">
```dts
function refreshAll({
includeLoadFunctions
}?: {
includeLoadFunctions?: boolean;
}): Promise<void>;
```
</div>
## replaceState
Programmatically replace the current history entry with the given `page.state`. To use the current URL, you can pass `''` as the first argument. Used for [shallow routing](/docs/kit/shallow-routing).
<div class="ts-block">
```dts
function replaceState(
url: string | URL,
state: App.PageState
): void;
```
</div>
# $app/paths
```js
// @noErrors
import { asset, assets, base, match, resolve, resolveRoute } from '$app/paths';
```
## asset
<blockquote class="since note">
Available since 2.26
</blockquote>
Resolve the URL of an asset in your `static` directory, by prefixing it with [`config.kit.paths.assets`](/docs/kit/configuration#paths) if configured, or otherwise by prefixing it with the base path.
During server rendering, the base path is relative and depends on the page currently being rendered.
```svelte
<script>
import { asset } from '$app/paths';
</script>
<img alt="a potato" src={asset('/potato.jpg')} />
```
<div class="ts-block">
```dts
function asset(file: Asset): string;
```
</div>
## assets
<blockquote class="tag deprecated note">
Use [`asset(...)`](/docs/kit/$app-paths#asset) instead
</blockquote>
An absolute path that matches [`config.kit.paths.assets`](/docs/kit/configuration#paths).
> [!NOTE] If a value for `config.kit.paths.assets` is specified, it will be replaced with `'/_svelte_kit_assets'` during `vite dev` or `vite preview`, since the assets don't yet live at their eventual URL.
<div class="ts-block">
```dts
let assets:
| ''
| `https://${string}`
| `http://${string}`
| '/_svelte_kit_assets';
```
</div>
## base
<blockquote class="tag deprecated note">
Use [`resolve(...)`](/docs/kit/$app-paths#resolve) instead
</blockquote>
A string that matches [`config.kit.paths.base`](/docs/kit/configuration#paths).
Example usage: `<a href="{base}/your-page">Link</a>`
<div class="ts-block">
```dts
let base: '' | `/${string}`;
```
</div>
## match
<blockquote class="since note">
Available since 2.52.0
</blockquote>
Match a path or URL to a route ID and extracts any parameters.
```js
// @errors: 7031
import { match } from '$app/paths';
const route = await match('/blog/hello-world');
if (route?.id === '/blog/[slug]') {
const slug = route.params.slug;
const response = await fetch(`/api/posts/${slug}`);
const post = await response.json();
}
```
<div class="ts-block">
```dts
function match(
url: Pathname_1 | URL | (string & {})
): Promise<{
id: RouteId;
params: Record<string, string>;
} | null>;
```
</div>
## resolve
<blockquote class="since note">
Available since 2.26
</blockquote>
Resolve a pathname by prefixing it with the base path, if any, or resolve a route ID by populating dynamic segments with parameters.
During server rendering, the base path is relative and depends on the page currently being rendered.
```js
// @errors: 7031
import { resolve } from '$app/paths';
// using a pathname
const resolved = resolve(`/blog/hello-world`);
// using a route ID plus parameters
const resolved = resolve('/blog/[slug]', {
slug: 'hello-world'
});
```
<div class="ts-block">
```dts
function resolve<
T extends
| RouteIdWithSearchOrHash
| PathnameWithSearchOrHash
>(...args: ResolveArgs<T>): ResolvedPathname;
```
</div>
## resolveRoute
<blockquote class="tag deprecated note">
Use [`resolve(...)`](/docs/kit/$app-paths#resolve) instead
</blockquote>
<div class="ts-block">
```dts
function resolveRoute<
T extends
| RouteIdWithSearchOrHash
| PathnameWithSearchOrHash
>(...args: ResolveArgs<T>): ResolvedPathname;
```
</div>
# $app/server
```js
// @noErrors
import {
command,
form,
getRequestEvent,
prerender,
query,
read,
requested
} from '$app/server';
```
## command
<blockquote class="since note">
Available since 2.27
</blockquote>
Creates a remote command. When called from the browser, the function will be invoked on the server via a `fetch` call.
See [Remote functions](/docs/kit/remote-functions#command) for full documentation.
<div class="ts-block">
```dts
function command<Output>(
fn: () => MaybePromise<Output>
): RemoteCommand<void, Output>;
```
</div>
<div class="ts-block">
```dts
function command<Input, Output>(
validate: 'unchecked',
fn: (arg: Input) => MaybePromise<Output>
): RemoteCommand<Input, Output>;
```
</div>
<div class="ts-block">
```dts
function command<Schema extends StandardSchemaV1, Output>(
validate: Schema,
fn: (
arg: StandardSchemaV1.InferOutput<Schema>
) => MaybePromise<Output>
): RemoteCommand<
StandardSchemaV1.InferInput<Schema>,
Output
>;
```
</div>
## form
<blockquote class="since note">
Available since 2.27
</blockquote>
Creates a form object that can be spread onto a `<form>` element.
See [Remote functions](/docs/kit/remote-functions#form) for full documentation.
<div class="ts-block">
```dts
function form<Output>(
fn: () => MaybePromise<Output>
): RemoteForm<void, Output>;
```
</div>
<div class="ts-block">
```dts
function form<Input extends RemoteFormInput, Output>(
validate: 'unchecked',
fn: (
data: Input,
issue: InvalidField<Input>
) => MaybePromise<Output>
): RemoteForm<Input, Output>;
```
</div>
<div class="ts-block">
```dts
function form<
Schema extends StandardSchemaV1<
RemoteFormInput,
Record<string, any>
>,
Output
>(
validate: Schema,
fn: (
data: StandardSchemaV1.InferOutput<Schema>,
issue: InvalidField<StandardSchemaV1.InferInput<Schema>>
) => MaybePromise<Output>
): RemoteForm<StandardSchemaV1.InferInput<Schema>, Output>;
```
</div>
## getRequestEvent
<blockquote class="since note">
Available since 2.20.0
</blockquote>
Returns the current `RequestEvent`. Can be used inside server hooks, server `load` functions, actions, and endpoints (and functions called by them).
In environments without [`AsyncLocalStorage`](https://nodejs.org/api/async_context.html#class-asynclocalstorage), this must be called synchronously (i.e. not after an `await`).
<div class="ts-block">
```dts
function getRequestEvent(): RequestEvent;
```
</div>
## prerender
<blockquote class="since note">
Available since 2.27
</blockquote>
Creates a remote prerender function. When called from the browser, the function will be invoked on the server via a `fetch` call.
See [Remote functions](/docs/kit/remote-functions#prerender) for full documentation.
<div class="ts-block">
```dts
function prerender<Output>(
fn: () => MaybePromise<Output>,
options?:
| {
inputs?: RemotePrerenderInputsGenerator<void>;
dynamic?: boolean;
}
| undefined
): RemotePrerenderFunction<void, Output>;
```
</div>
<div class="ts-block">
```dts
function prerender<Input, Output>(
validate: 'unchecked',
fn: (arg: Input) => MaybePromise<Output>,
options?:
| {
inputs?: RemotePrerenderInputsGenerator<Input>;
dynamic?: boolean;
}
| undefined
): RemotePrerenderFunction<Input, Output>;
```
</div>
<div class="ts-block">
```dts
function prerender<Schema extends StandardSchemaV1, Output>(
schema: Schema,
fn: (
arg: StandardSchemaV1.InferOutput<Schema>
) => MaybePromise<Output>,
options?:
| {
inputs?: RemotePrerenderInputsGenerator<
StandardSchemaV1.InferInput<Schema>
>;
dynamic?: boolean;
}
| undefined
): RemotePrerenderFunction<
StandardSchemaV1.InferInput<Schema>,
Output
>;
```
</div>
## query
<blockquote class="since note">
Available since 2.27
</blockquote>
Creates a remote query. When called from the browser, the function will be invoked on the server via a `fetch` call.
See [Remote functions](/docs/kit/remote-functions#query) for full documentation.
<div class="ts-block">
```dts
function query<Output>(
fn: () => MaybePromise<Output>
): RemoteQueryFunction<void, Output>;
```
</div>
<div class="ts-block">
```dts
function query<Input, Output>(
validate: 'unchecked',
fn: (arg: Input) => MaybePromise<Output>
): RemoteQueryFunction<Input, Output>;
```
</div>
<div class="ts-block">
```dts
function query<Schema extends StandardSchemaV1, Output>(
schema: Schema,
fn: (
arg: StandardSchemaV1.InferOutput<Schema>
) => MaybePromise<Output>
): RemoteQueryFunction<
StandardSchemaV1.InferInput<Schema>,
Output,
StandardSchemaV1.InferOutput<Schema>
>;
```
</div>
## read
<blockquote class="since note">
Available since 2.4.0
</blockquote>
Read the contents of an imported asset from the filesystem
```js
// @errors: 7031
import { read } from '$app/server';
import somefile from './somefile.txt';
const asset = read(somefile);
const text = await asset.text();
```
<div class="ts-block">
```dts
function read(asset: string): Response;
```
</div>
## requested
In the context of a remote `command` or `form` request, returns an iterable
of `{ arg, query }` entries for the refreshes requested by the client, up to
the supplied `limit`. Each `query` is a `RemoteQuery` bound to the original
client-side cache key, so `refresh()` / `set()` propagate correctly even when
the query's schema transforms the input. `arg` is the *validated* argument,
i.e. the value after the schema has run (so `InferOutput<Schema>` for queries
declared with a Standard Schema).
Arguments that fail validation or exceed `limit` are recorded as failures in
the response to the client.
```ts
import { requested } from '$app/server';
for (const { arg, query } of requested(getPost, 5)) {
// `arg` is the validated argument; `query` is bound to the client's
// cache key. It's safe to throw away this promise -- SvelteKit will
// await it and forward any errors to the client.
void query.refresh();
}
```
As a shorthand for the above, you can also call `refreshAll` on the result:
```ts
import { requested } from '$app/server';
await requested(getPost, 5).refreshAll();
```
Works with `query.batch` as well — refreshes for individual entries are
collected into a single batched call.
For live queries, the same applies, but with `reconnect` and `reconnectAll`.
<div class="ts-block">
```dts
function requested<Input, Output, Validated = Input>(
query: RemoteQueryFunction<Input, Output, Validated>,
limit: number
): QueryRequestedResult<Validated, Output>;
```
</div>
<div class="ts-block">
```dts
function requested<Input, Output, Validated = Input>(
query: RemoteLiveQueryFunction<Input, Output, Validated>,
limit: number
): LiveQueryRequestedResult<Validated, Output>;
```
</div>
## query
<div class="ts-block">
```dts
namespace query {
/**
* Creates a batch query function that collects multiple calls and executes them in a single request
*
* See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query.batch) for full documentation.
*
* @since 2.35
*/
function batch<Input, Output>(
validate: 'unchecked',
fn: (
args: Input[]
) => MaybePromise<(arg: Input, idx: number) => Output>
): RemoteQueryFunction<Input, Output>;
/**
* Creates a batch query function that collects multiple calls and executes them in a single request
*
* See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query.batch) for full documentation.
*
* @since 2.35
*/
function batch<Schema extends StandardSchemaV1, Output>(
schema: Schema,
fn: (
args: StandardSchemaV1.InferOutput<Schema>[]
) => MaybePromise<
(
arg: StandardSchemaV1.InferOutput<Schema>,
idx: number
) => Output
>
): RemoteQueryFunction<
StandardSchemaV1.InferInput<Schema>,
Output,
StandardSchemaV1.InferOutput<Schema>
>;
/**
* Creates a live remote query. When called from the browser, the function will be invoked on the server via a streaming `fetch` call.
*
* See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query.live) for full documentation.
*
* */
function live<Output>(
fn: (
arg: void
) => RemoteLiveQueryUserFunctionReturnType<Output>
): RemoteLiveQueryFunction<void, Output>;
function live<Input, Output>(
validate: 'unchecked',
fn: (
arg: Input
) => RemoteLiveQueryUserFunctionReturnType<Output>
): RemoteLiveQueryFunction<Input, Output>;
function live<Schema extends StandardSchemaV1, Output>(
schema: Schema,
fn: (
arg: StandardSchemaV1.InferOutput<Schema>
) => RemoteLiveQueryUserFunctionReturnType<Output>
): RemoteLiveQueryFunction<
StandardSchemaV1.InferInput<Schema>,
Output,
StandardSchemaV1.InferOutput<Schema>
>;
}
```
</div>
# $app/state
SvelteKit makes three read-only state objects available via the `$app/state` module — `page`, `navigating` and `updated`.
> [!NOTE]
> This module was added in 2.12. If you're using an earlier version of SvelteKit, use [`$app/stores`]($app-stores) instead.
```js
// @noErrors
import { navigating, page, updated } from '$app/state';
```
## navigating
A read-only object representing an in-progress navigation, with `from`, `to`, `type` and (if `type === 'popstate'`) `delta` properties.
Values are `null` when no navigation is occurring, or during server rendering.
<div class="ts-block">
```dts
const navigating:
| import('@sveltejs/kit').Navigation
| {
from: null;
to: null;
type: null;
willUnload: null;
delta: null;
complete: null;
};
```
</div>
## page
A read-only reactive object with information about the current page, serving several use cases:
- retrieving the combined `data` of all pages/layouts anywhere in your component tree (also see [loading data](/docs/kit/load))
- retrieving the current value of the `form` prop anywhere in your component tree (also see [form actions](/docs/kit/form-actions))
- retrieving the page state that was set through `goto`, `pushState` or `replaceState` (also see [goto](/docs/kit/$app-navigation#goto) and [shallow routing](/docs/kit/shallow-routing))
- retrieving metadata such as the URL you're on, the current route and its parameters, and whether or not there was an error
```svelte
<!--- file: +layout.svelte --->
<script>
import { page } from '$app/state';
</script>
<p>Currently at {page.url.pathname}</p>
{#if page.error}
<span class="red">Problem detected</span>
{:else}
<span class="small">All systems operational</span>
{/if}
```
Changes to `page` are available exclusively with runes. (The legacy reactivity syntax will not reflect any changes)
```svelte
<!--- file: +page.svelte --->
<script>
import { page } from '$app/state';
const id = $derived(page.params.id); // This will correctly update id for usage on this page
$: badId = page.params.id; // Do not use; will never update after initial load
</script>
```
On the server, values can only be read during rendering (in other words _not_ in e.g. `load` functions). In the browser, the values can be read at any time.
<div class="ts-block">
```dts
const page: import('@sveltejs/kit').Page;
```
</div>
## updated
A read-only reactive value that's initially `false`. If [`version.pollInterval`](/docs/kit/configuration#version) is a non-zero value, SvelteKit will poll for new versions of the app and update `current` to `true` when it detects one. `updated.check()` will force an immediate check, regardless of polling.
<div class="ts-block">
```dts
const updated: {
get current(): boolean;
check(): Promise<boolean>;
};
```
</div>
# $app/stores
This module contains store-based equivalents of the exports from [`$app/state`]($app-state). If you're using SvelteKit 2.12 or later, use that module instead.
```js
// @noErrors
import { getStores, navigating, page, updated } from '$app/stores';
```
## getStores
<div class="ts-block">
```dts
function getStores(): {
page: typeof page;
navigating: typeof navigating;
updated: typeof updated;
};
```
</div>
## navigating
<blockquote class="tag deprecated note">
Use `navigating` from `$app/state` instead (requires Svelte 5, [see docs for more info](/docs/kit/migrating-to-sveltekit-2#SvelteKit-2.12:-$app-stores-deprecated))
</blockquote>
A readable store.
When navigating starts, its value is a `Navigation` object with `from`, `to`, `type` and (if `type === 'popstate'`) `delta` properties.
When navigating finishes, its value reverts to `null`.
On the server, this store can only be subscribed to during component initialization. In the browser, it can be subscribed to at any time.
<div class="ts-block">
```dts
const navigating: import('svelte/store').Readable<
import('@sveltejs/kit').Navigation | null
>;
```
</div>
## page
<blockquote class="tag deprecated note">
Use `page` from `$app/state` instead (requires Svelte 5, [see docs for more info](/docs/kit/migrating-to-sveltekit-2#SvelteKit-2.12:-$app-stores-deprecated))
</blockquote>
A readable store whose value contains page data.
On the server, this store can only be subscribed to during component initialization. In the browser, it can be subscribed to at any time.
<div class="ts-block">
```dts
const page: import('svelte/store').Readable<
import('@sveltejs/kit').Page
>;
```
</div>
## updated
<blockquote class="tag deprecated note">
Use `updated` from `$app/state` instead (requires Svelte 5, [see docs for more info](/docs/kit/migrating-to-sveltekit-2#SvelteKit-2.12:-$app-stores-deprecated))
</blockquote>
A readable store whose initial value is `false`. If [`version.pollInterval`](/docs/kit/configuration#version) is a non-zero value, SvelteKit will poll for new versions of the app and update the store value to `true` when it detects one. `updated.check()` will force an immediate check, regardless of polling.
On the server, this store can only be subscribed to during component initialization. In the browser, it can be subscribed to at any time.
<div class="ts-block">
```dts
const updated: import('svelte/store').Readable<boolean> & {
check(): Promise<boolean>;
};
```
</div>
# $app/types
This module contains generated types for the routes in your app.
<blockquote class="since note">
<p>Available since 2.26</p>
</blockquote>
```js
// @noErrors
import type { RouteId, RouteParams, LayoutParams } from '$app/types';
```
## Asset
A union of all the filenames of assets contained in your `static` directory, plus a `string` wildcard for asset paths generated from `import` declarations.
<div class="ts-block">
```dts
type Asset = '/favicon.png' | '/robots.txt' | (string & {});
```
</div>
## RouteId
A union of all the route IDs in your app. Used for `page.route.id` and `event.route.id`.
<div class="ts-block">
```dts
type RouteId = '/' | '/my-route' | '/my-other-route/[param]';
```
</div>
## Pathname
A union of all valid pathnames in your app.
<div class="ts-block">
```dts
type Pathname = '/' | '/my-route' | `/my-other-route/${string}` & {};
```
</div>
## ResolvedPathname
Similar to `Pathname`, but possibly prefixed with a [base path](configuration#paths). Used for `page.url.pathname`.
<div class="ts-block">
```dts
type ResolvedPathname = `${'' | `/${string}`}/` | `${'' | `/${string}`}/my-route` | `${'' | `/${string}`}/my-other-route/${string}` | {};
```
</div>
## RouteParams
A utility for getting the parameters associated with a given route.
```ts
// @errors: 2552
type BlogParams = RouteParams<'/blog/[slug]'>; // { slug: string }
```
<div class="ts-block">
```dts
type RouteParams<T extends RouteId> = { /* generated */ } | Record<string, never>;
```
</div>
## LayoutParams
A utility for getting the parameters associated with a given layout, which is similar to `RouteParams` but also includes optional parameters for any child route.
<div class="ts-block">
```dts
type RouteParams<T extends RouteId> = { /* generated */ } | Record<string, never>;
```
</div>
# $env/dynamic/private
This module provides access to environment variables set _dynamically_ at runtime and that are limited to _private_ access.
| | Runtime | Build time |
| ------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Private | [`$env/dynamic/private`](/docs/kit/$env-dynamic-private) | [`$env/static/private`](/docs/kit/$env-static-private) |
| Public | [`$env/dynamic/public`](/docs/kit/$env-dynamic-public) | [`$env/static/public`](/docs/kit/$env-static-public) |
Dynamic environment variables are defined by the platform you're running on. For example if you're using [`adapter-node`](https://github.com/sveltejs/kit/tree/main/packages/adapter-node) (or running [`vite preview`](/docs/kit/cli)), this is equivalent to `process.env`.
**_Private_ access:**
- This module cannot be imported into client-side code
- This module includes variables that _do not_ begin with [`config.kit.env.publicPrefix`](/docs/kit/configuration#env) _and do_ start with [`config.kit.env.privatePrefix`](/docs/kit/configuration#env) (if configured)
> [!NOTE] In `dev`, `$env/dynamic` includes environment variables from `.env`. In `prod`, this behavior will depend on your adapter.
> [!NOTE] To get correct types, environment variables referenced in your code should be declared (for example in an `.env` file), even if they don't have a value until the app is deployed:
>
> ```env
> MY_FEATURE_FLAG=
> ```
>
> You can override `.env` values from the command line like so:
>
> ```sh
> MY_FEATURE_FLAG="enabled" npm run dev
> ```
For example, given the following runtime environment:
```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://site.com
```
With the default `publicPrefix` and `privatePrefix`:
```ts
import { env } from '$env/dynamic/private';
console.log(env.ENVIRONMENT); // => "production"
console.log(env.PUBLIC_BASE_URL); // => undefined
```
# $env/dynamic/public
This module provides access to environment variables set _dynamically_ at runtime and that are _publicly_ accessible.
| | Runtime | Build time |
| ------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Private | [`$env/dynamic/private`](/docs/kit/$env-dynamic-private) | [`$env/static/private`](/docs/kit/$env-static-private) |
| Public | [`$env/dynamic/public`](/docs/kit/$env-dynamic-public) | [`$env/static/public`](/docs/kit/$env-static-public) |
Dynamic environment variables are defined by the platform you're running on. For example if you're using [`adapter-node`](https://github.com/sveltejs/kit/tree/main/packages/adapter-node) (or running [`vite preview`](/docs/kit/cli)), this is equivalent to `process.env`.
**_Public_ access:**
- This module _can_ be imported into client-side code
- **Only** variables that begin with [`config.kit.env.publicPrefix`](/docs/kit/configuration#env) (which defaults to `PUBLIC_`) are included
> [!NOTE] In `dev`, `$env/dynamic` includes environment variables from `.env`. In `prod`, this behavior will depend on your adapter.
> [!NOTE] To get correct types, environment variables referenced in your code should be declared (for example in an `.env` file), even if they don't have a value until the app is deployed:
>
> ```env
> MY_FEATURE_FLAG=
> ```
>
> You can override `.env` values from the command line like so:
>
> ```sh
> MY_FEATURE_FLAG="enabled" npm run dev
> ```
For example, given the following runtime environment:
```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://example.com
```
With the default `publicPrefix` and `privatePrefix`:
```ts
import { env } from '$env/dynamic/public';
console.log(env.ENVIRONMENT); // => undefined, not public
console.log(env.PUBLIC_BASE_URL); // => "http://example.com"
```
```
```
# $env/static/private
This module provides access to environment variables that are injected _statically_ into your bundle at build time and are limited to _private_ access.
| | Runtime | Build time |
| ------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Private | [`$env/dynamic/private`](/docs/kit/$env-dynamic-private) | [`$env/static/private`](/docs/kit/$env-static-private) |
| Public | [`$env/dynamic/public`](/docs/kit/$env-dynamic-public) | [`$env/static/public`](/docs/kit/$env-static-public) |
Static environment variables are [loaded by Vite](https://vitejs.dev/guide/env-and-mode.html#env-files) from `.env` files and `process.env` at build time and then statically injected into your bundle at build time, enabling optimisations like dead code elimination.
**_Private_ access:**
- This module cannot be imported into client-side code
- This module only includes variables that _do not_ begin with [`config.kit.env.publicPrefix`](/docs/kit/configuration#env) _and do_ start with [`config.kit.env.privatePrefix`](/docs/kit/configuration#env) (if configured)
For example, given the following build time environment:
```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://site.com
```
With the default `publicPrefix` and `privatePrefix`:
```ts
import { ENVIRONMENT, PUBLIC_BASE_URL } from '$env/static/private';
console.log(ENVIRONMENT); // => "production"
console.log(PUBLIC_BASE_URL); // => throws error during build
```
The above values will be the same _even if_ different values for `ENVIRONMENT` or `PUBLIC_BASE_URL` are set at runtime, as they are statically replaced in your code with their build time values.
# $env/static/public
This module provides access to environment variables that are injected _statically_ into your bundle at build time and are _publicly_ accessible.
| | Runtime | Build time |
| ------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Private | [`$env/dynamic/private`](/docs/kit/$env-dynamic-private) | [`$env/static/private`](/docs/kit/$env-static-private) |
| Public | [`$env/dynamic/public`](/docs/kit/$env-dynamic-public) | [`$env/static/public`](/docs/kit/$env-static-public) |
Static environment variables are [loaded by Vite](https://vitejs.dev/guide/env-and-mode.html#env-files) from `.env` files and `process.env` at build time and then statically injected into your bundle at build time, enabling optimisations like dead code elimination.
**_Public_ access:**
- This module _can_ be imported into client-side code
- **Only** variables that begin with [`config.kit.env.publicPrefix`](/docs/kit/configuration#env) (which defaults to `PUBLIC_`) are included
For example, given the following build time environment:
```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://site.com
```
With the default `publicPrefix` and `privatePrefix`:
```ts
import { ENVIRONMENT, PUBLIC_BASE_URL } from '$env/static/public';
console.log(ENVIRONMENT); // => throws error during build
console.log(PUBLIC_BASE_URL); // => "http://site.com"
```
The above values will be the same _even if_ different values for `ENVIRONMENT` or `PUBLIC_BASE_URL` are set at runtime, as they are statically replaced in your code with their build time values.
# $lib
SvelteKit automatically makes files under `src/lib` available using the `$lib` import alias.
```svelte
<!--- file: src/lib/Component.svelte --->
A reusable component
```
```svelte
<!--- file: src/routes/+page.svelte --->
<script>
import Component from '$lib/Component.svelte';
</script>
<Component />
```
# $service-worker
```js
// @noErrors
import { base, build, files, prerendered, version } from '$service-worker';
```
This module is only available to [service workers](/docs/kit/service-workers).
## base
The `base` path of the deployment. Typically this is equivalent to `config.kit.paths.base`, but it is calculated from `location.pathname` meaning that it will continue to work correctly if the site is deployed to a subdirectory.
Note that there is a `base` but no `assets`, since service workers cannot be used if `config.kit.paths.assets` is specified.
<div class="ts-block">
```dts
const base: string;
```
</div>
## build
An array of URL strings representing the files generated by Vite, suitable for caching with `cache.addAll(build)`.
During development, this is an empty array.
<div class="ts-block">
```dts
const build: string[];
```
</div>
## files
An array of URL strings representing the files in your static directory, or whatever directory is specified by `config.kit.files.assets`. You can customize which files are included from `static` directory using [`config.kit.serviceWorker.files`](/docs/kit/configuration#serviceWorker)
<div class="ts-block">
```dts
const files: string[];
```
</div>
## prerendered
An array of pathnames corresponding to prerendered pages and endpoints.
During development, this is an empty array.
<div class="ts-block">
```dts
const prerendered: string[];
```
</div>
## version
See [`config.kit.version`](/docs/kit/configuration#version). It's useful for generating unique cache names inside your service worker, so that a later deployment of your app can invalidate old caches.
<div class="ts-block">
```dts
const version: string;
```
</div>
# Configuration
Your project's configuration lives in a `svelte.config.js` file at the root of your project. As well as SvelteKit, this config object is used by other tooling that integrates with Svelte such as editor extensions.
```js
/// file: svelte.config.js
// @filename: ambient.d.ts
declare module '@sveltejs/adapter-auto' {
const plugin: () => import('@sveltejs/kit').Adapter;
export default plugin;
}
// @filename: index.js
// ---cut---
import adapter from '@sveltejs/adapter-auto';
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
adapter: adapter()
}
};
export default config;
```
## Config
An extension of [`vite-plugin-svelte`'s options](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/config.md#svelte-options).
<div class="ts-block">
```dts
interface Config extends SvelteConfig {/*…*/}
```
<div class="ts-block-property">
```dts
kit?: KitConfig;
```
<div class="ts-block-property-details">
SvelteKit options.
</div>
</div>
<div class="ts-block-property">
```dts
[key: string]: any;
```
<div class="ts-block-property-details">
Any additional options required by tooling that integrates with Svelte.
</div>
</div></div>
## KitConfig
The `kit` property configures SvelteKit, and can have the following properties:
## adapter
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `undefined`
</div>
Your [adapter](/docs/kit/adapters) is run when executing `vite build`. It determines how the output is converted for different platforms.
<div class="ts-block-property-children">
</div>
## alias
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `{}`
</div>
An object containing zero or more aliases used to replace values in `import` statements. These aliases are automatically passed to Vite and TypeScript.
```js
// @errors: 7031
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
alias: {
// this will match a file
'my-file': 'path/to/my-file.js',
// this will match a directory and its contents
// (`my-directory/x` resolves to `path/to/my-directory/x`)
'my-directory': 'path/to/my-directory',
// an alias ending /* will only match
// the contents of a directory, not the directory itself
'my-directory/*': 'path/to/my-directory/*'
}
}
};
```
> [!NOTE] You will need to run `npm run dev` to have SvelteKit automatically generate the required alias configuration in `jsconfig.json` or `tsconfig.json`.
<div class="ts-block-property-children">
</div>
## appDir
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"_app"`
</div>
The directory where SvelteKit keeps its stuff, including static assets (such as JS and CSS) and internally-used routes.
If `paths.assets` is specified, there will be two app directories — `${paths.assets}/${appDir}` and `${paths.base}/${appDir}`.
<div class="ts-block-property-children">
</div>
## csp
<div class="ts-block-property-bullets">
</div>
[Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy) configuration. CSP helps to protect your users against cross-site scripting (XSS) attacks, by limiting the places resources can be loaded from. For example, a configuration like this...
```js
// @errors: 7031
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
csp: {
directives: {
'script-src': ['self']
},
// must be specified with either the `report-uri` or `report-to` directives, or both
reportOnly: {
'script-src': ['self'],
'report-uri': ['/']
}
}
}
};
export default config;
```
...would prevent scripts loading from external sites. SvelteKit will augment the specified directives with nonces or hashes (depending on `mode`) for any inline styles and scripts it generates.
To add a nonce for scripts and links manually included in `src/app.html`, you may use the placeholder `%sveltekit.nonce%` (for example `<script nonce="%sveltekit.nonce%">`).
When pages are prerendered, the CSP header is added via a `<meta http-equiv>` tag (note that in this case, `frame-ancestors`, `report-uri` and `sandbox` directives will be ignored).
> [!NOTE] When `mode` is `'auto'`, SvelteKit will use nonces for dynamically rendered pages and hashes for prerendered pages. Using nonces with prerendered pages is insecure and therefore forbidden.
> [!NOTE] Note that most [Svelte transitions](/tutorial/svelte/transition) work by creating an inline `<style>` element. If you use these in your app, you must either leave the `style-src` directive unspecified or add `unsafe-inline`.
If this level of configuration is insufficient and you have more dynamic requirements, you can use the [`handle` hook](/docs/kit/hooks#Server-hooks-handle) to roll your own CSP.
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
mode?: 'hash' | 'nonce' | 'auto';
```
<div class="ts-block-property-details">
Whether to use hashes or nonces to restrict `<script>` and `<style>` elements. `'auto'` will use hashes for prerendered pages, and nonces for dynamically rendered pages.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
directives?: CspDirectives;
```
<div class="ts-block-property-details">
Directives that will be added to `Content-Security-Policy` headers.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
reportOnly?: CspDirectives;
```
<div class="ts-block-property-details">
Directives that will be added to `Content-Security-Policy-Report-Only` headers.
</div>
</div>
</div>
## csrf
<div class="ts-block-property-bullets">
</div>
Protection against [cross-site request forgery (CSRF)](https://owasp.org/www-community/attacks/csrf) attacks.
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
checkOrigin?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `true`
- <span class="tag deprecated">deprecated</span> Use `trustedOrigins: ['*']` instead
</div>
Whether to check the incoming `origin` header for `POST`, `PUT`, `PATCH`, or `DELETE` form submissions and verify that it matches the server's origin.
To allow people to make `POST`, `PUT`, `PATCH`, or `DELETE` requests with a `Content-Type` of `application/x-www-form-urlencoded`, `multipart/form-data`, or `text/plain` to your app from other origins, you will need to disable this option. Be careful!
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
trustedOrigins?: string[];
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `[]`
</div>
An array of origins that are allowed to make cross-origin form submissions to your app.
Each origin should be a complete origin including protocol (e.g., `https://payment-gateway.com`).
This is useful for allowing trusted third-party services like payment gateways or authentication providers to submit forms to your app.
If the array contains `'*'`, all origins will be trusted. This is generally not recommended!
> [!NOTE] Only add origins you completely trust, as this bypasses CSRF protection for those origins.
CSRF checks only apply in production, not in local development.
</div>
</div>
</div>
## embedded
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
</div>
Whether or not the app is embedded inside a larger app. If `true`, SvelteKit will add its event listeners related to navigation etc on the parent of `%sveltekit.body%` instead of `window`, and will pass `params` from the server rather than inferring them from `location.pathname`.
Note that it is generally not supported to embed multiple SvelteKit apps on the same page and use client-side SvelteKit features within them (things such as pushing to the history state assume a single instance).
<div class="ts-block-property-children">
</div>
## env
<div class="ts-block-property-bullets">
</div>
Environment variable configuration
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
dir?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"."`
</div>
The directory to search for `.env` files.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
publicPrefix?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"PUBLIC_"`
</div>
A prefix that signals that an environment variable is safe to expose to client-side code. See [`$env/static/public`](/docs/kit/$env-static-public) and [`$env/dynamic/public`](/docs/kit/$env-dynamic-public). Note that Vite's [`envPrefix`](https://vitejs.dev/config/shared-options.html#envprefix) must be set separately if you are using Vite's environment variable handling - though use of that feature should generally be unnecessary.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
privatePrefix?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `""`
- <span class="tag since">available since</span> v1.21.0
</div>
A prefix that signals that an environment variable is unsafe to expose to client-side code. Environment variables matching neither the public nor the private prefix will be discarded completely. See [`$env/static/private`](/docs/kit/$env-static-private) and [`$env/dynamic/private`](/docs/kit/$env-dynamic-private).
</div>
</div>
</div>
## experimental
<div class="ts-block-property-bullets">
</div>
Experimental features. Here be dragons. These are not subject to semantic versioning, so breaking changes or removal can happen in any release.
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
tracing?: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `{ server: false, serverFile: false }`
- <span class="tag since">available since</span> v2.31.0
</div>
Options for enabling server-side [OpenTelemetry](https://opentelemetry.io/) tracing for SvelteKit operations including the [`handle` hook](/docs/kit/hooks#Server-hooks-handle), [`load` functions](/docs/kit/load), [form actions](/docs/kit/form-actions), and [remote functions](/docs/kit/remote-functions).
<div class="ts-block-property-children"><div class="ts-block-property">
```ts
// @noErrors
server?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
- <span class="tag since">available since</span> v2.31.0
</div>
Enables server-side [OpenTelemetry](https://opentelemetry.io/) span emission for SvelteKit operations including the [`handle` hook](/docs/kit/hooks#Server-hooks-handle), [`load` functions](/docs/kit/load), [form actions](/docs/kit/form-actions), and [remote functions](/docs/kit/remote-functions).
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
instrumentation?: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag since">available since</span> v2.31.0
</div>
<div class="ts-block-property-children"><div class="ts-block-property">
```ts
// @noErrors
server?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
- <span class="tag since">available since</span> v2.31.0
</div>
Enables `instrumentation.server.js` for tracing and observability instrumentation.
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
remoteFunctions?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
</div>
Whether to enable the experimental remote functions feature. This feature is not yet stable and may be changed or removed at any time.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
forkPreloads?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
</div>
Whether to enable the experimental forked preloading feature using Svelte's fork API.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
handleRenderingErrors?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `false`
</div>
Whether to enable the experimental handling of rendering errors.
When enabled, `<svelte:boundary>` is used to wrap components at each level
where there's an `+error.svelte`, rendering the error page if the component fails.
In addition, error boundaries also work on the server and the error object goes through `handleError`.
</div>
</div>
</div>
## files
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
</div>
Where to find various files within your project.
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
src?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src"`
- <span class="tag since">available since</span> v2.28
</div>
The location of your source code.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
assets?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"static"`
</div>
A place to put static files that should have stable URLs and undergo no processing, such as `favicon.ico` or `manifest.json`.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
hooks?: {/*…*/}
```
<div class="ts-block-property-details">
<div class="ts-block-property-children"><div class="ts-block-property">
```ts
// @noErrors
client?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/hooks.client"`
</div>
The location of your client [hooks](/docs/kit/hooks).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
server?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/hooks.server"`
</div>
The location of your server [hooks](/docs/kit/hooks).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
universal?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/hooks"`
- <span class="tag since">available since</span> v2.3.0
</div>
The location of your universal [hooks](/docs/kit/hooks).
</div>
</div></div>
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
lib?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/lib"`
</div>
Your app's internal library, accessible throughout the codebase as `$lib`.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
params?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/params"`
</div>
A directory containing [parameter matchers](/docs/kit/advanced-routing#Matching).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
routes?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/routes"`
</div>
The files that define the structure of your app (see [Routing](/docs/kit/routing)).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
serviceWorker?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/service-worker"`
</div>
The location of your service worker's entry point (see [Service workers](/docs/kit/service-workers)).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
appTemplate?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/app.html"`
</div>
The location of the template for HTML responses.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
errorTemplate?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag deprecated">deprecated</span> this feature is still supported, but it's generally recommended to use [monorepos](https://levelup.video/tutorials/monorepos-with-pnpm) instead
- <span class="tag">default</span> `"src/error.html"`
</div>
The location of the template for fallback error responses.
</div>
</div>
</div>
## inlineStyleThreshold
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `0`
</div>
Inline CSS inside a `<style>` block at the head of the HTML. This option is a number that specifies the maximum length of a CSS file in UTF-16 code units, as specified by the [String.length](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length) property, to be inlined. All CSS files needed for the page that are smaller than this value are merged and inlined in a `<style>` block.
> [!NOTE] This results in fewer initial requests and can improve your [First Contentful Paint](https://web.dev/first-contentful-paint) score. However, it generates larger HTML output and reduces the effectiveness of browser caches. Use it advisedly.
<div class="ts-block-property-children">
</div>
## moduleExtensions
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `[".js", ".ts"]`
</div>
An array of file extensions that SvelteKit will treat as modules. Files with extensions that match neither `config.extensions` nor `config.kit.moduleExtensions` will be ignored by the router.
<div class="ts-block-property-children">
</div>
## outDir
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `".svelte-kit"`
</div>
The directory that SvelteKit writes files to during `dev` and `build`. You should exclude this directory from version control.
<div class="ts-block-property-children">
</div>
## output
<div class="ts-block-property-bullets">
</div>
Options related to the build output format
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
preloadStrategy?: 'modulepreload' | 'preload-js' | 'preload-mjs';
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"modulepreload"`
- <span class="tag since">available since</span> v1.8.4
</div>
SvelteKit will preload the JavaScript modules needed for the initial page to avoid import 'waterfalls', resulting in faster application startup. There
are three strategies with different trade-offs:
- `modulepreload` - uses `<link rel="modulepreload">`. This delivers the best results in Chromium-based browsers, in Firefox 115+, and Safari 17+. It is ignored in older browsers.
- `preload-js` - uses `<link rel="preload">`. Prevents waterfalls in Chromium and Safari, but Chromium will parse each module twice (once as a script, once as a module). Causes modules to be requested twice in Firefox. This is a good setting if you want to maximise performance for users on iOS devices at the cost of a very slight degradation for Chromium users.
- `preload-mjs` - uses `<link rel="preload">` but with the `.mjs` extension which prevents double-parsing in Chromium. Some static webservers will fail to serve .mjs files with a `Content-Type: application/javascript` header, which will cause your application to break. If that doesn't apply to you, this is the option that will deliver the best performance for the largest number of users, until `modulepreload` is more widely supported.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
bundleStrategy?: 'split' | 'single' | 'inline';
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `'split'`
- <span class="tag since">available since</span> v2.13.0
</div>
The bundle strategy option affects how your app's JavaScript and CSS files are loaded.
- If `'split'`, splits the app up into multiple .js/.css files so that they are loaded lazily as the user navigates around the app. This is the default, and is recommended for most scenarios.
- If `'single'`, creates just one .js bundle and one .css file containing code for the entire app.
- If `'inline'`, inlines all JavaScript and CSS of the entire app into the HTML. The result is usable without a server (i.e. you can just open the file in your browser).
When using `'split'`, you can also adjust the bundling behaviour by setting [`output.experimentalMinChunkSize`](https://rollupjs.org/configuration-options/#output-experimentalminchunksize) and [`output.manualChunks`](https://rollupjs.org/configuration-options/#output-manualchunks) inside your Vite config's [`build.rollupOptions`](https://vite.dev/config/build-options.html#build-rollupoptions).
If you want to inline your assets, you'll need to set Vite's [`build.assetsInlineLimit`](https://vite.dev/config/build-options.html#build-assetsinlinelimit) option to an appropriate size then import your assets through Vite.
```js
// @errors: 7031
/// file: vite.config.js
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';
export default defineConfig({
plugins: [sveltekit()],
build: {
// inline all imported assets
assetsInlineLimit: Infinity
}
});
```
```svelte
/// file: src/routes/+layout.svelte
<script>
// import the asset through Vite
import favicon from './favicon.png';
</script>
<svelte:head>
<!-- this asset will be inlined as a base64 URL -->
<link rel="icon" href={favicon} />
</svelte:head>
```
</div>
</div>
</div>
## paths
<div class="ts-block-property-bullets">
</div>
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
assets?: '' | `http://${string}` | `https://${string}`;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `""`
</div>
An absolute path that your app's files are served from. This is useful if your files are served from a storage bucket of some kind.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
base?: '' | `/${string}`;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `""`
</div>
A root-relative path that must start, but not end with `/` (e.g. `/base-path`), unless it is the empty string. This specifies where your app is served from and allows the app to live on a non-root path. Note that you need to prepend all your root-relative links with the base value or they will point to the root of your domain, not your `base` (this is how the browser works). You can use [`base` from `$app/paths`](/docs/kit/$app-paths#base) for that: `<a href="{base}/your-page">Link</a>`. If you find yourself writing this often, it may make sense to extract this into a reusable component.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
relative?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `true`
- <span class="tag since">available since</span> v1.9.0
</div>
Whether to use relative asset paths.
If `true`, `base` and `assets` imported from `$app/paths` will be replaced with relative asset paths during server-side rendering, resulting in more portable HTML.
If `false`, `%sveltekit.assets%` and references to build artifacts will always be root-relative paths, unless `paths.assets` is an external URL
[Single-page app](/docs/kit/single-page-apps) fallback pages will always use absolute paths, regardless of this setting.
If your app uses a `<base>` element, you should set this to `false`, otherwise asset URLs will incorrectly be resolved against the `<base>` URL rather than the current page.
In 1.0, `undefined` was a valid value, which was set by default. In that case, if `paths.assets` was not external, SvelteKit would replace `%sveltekit.assets%` with a relative path and use relative paths to reference build artifacts, but `base` and `assets` imported from `$app/paths` would be as specified in your config.
</div>
</div>
</div>
## prerender
<div class="ts-block-property-bullets">
</div>
See [Prerendering](/docs/kit/page-options#prerender).
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
concurrency?: number;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `1`
</div>
How many pages can be prerendered simultaneously. JS is single-threaded, but in cases where prerendering performance is network-bound (for example loading content from a remote CMS) this can speed things up by processing other tasks while waiting on the network response.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
crawl?: boolean;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `true`
</div>
Whether SvelteKit should find pages to prerender by following links from `entries`.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
entries?: Array<'*' | `/${string}`>;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `["*"]`
</div>
An array of pages to prerender, or start crawling from (if `crawl: true`). The `*` string includes all routes containing no required `[parameters]` with optional parameters included as being empty (since SvelteKit doesn't know what value any parameters should have).
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
handleHttpError?: PrerenderHttpErrorHandlerValue;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"fail"`
- <span class="tag since">available since</span> v1.15.7
</div>
How to respond to HTTP errors encountered while prerendering the app.
- `'fail'` — fail the build
- `'ignore'` - silently ignore the failure and continue
- `'warn'` — continue, but print a warning
- `(details) => void` — a custom error handler that takes a `details` object with `status`, `path`, `referrer`, `referenceType` and `message` properties. If you `throw` from this function, the build will fail
```js
// @errors: 7031
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
kit: {
prerender: {
handleHttpError: ({ path, referrer, message }) => {
// ignore deliberate link to shiny 404 page
if (path === '/not-found' && referrer === '/blog/how-we-built-our-404-page') {
return;
}
// otherwise fail the build
throw new Error(message);
}
}
}
};
```
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
handleMissingId?: PrerenderMissingIdHandlerValue;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"fail"`
- <span class="tag since">available since</span> v1.15.7
</div>
How to respond when hash links from one prerendered page to another don't correspond to an `id` on the destination page.
- `'fail'` — fail the build
- `'ignore'` - silently ignore the failure and continue
- `'warn'` — continue, but print a warning
- `(details) => void` — a custom error handler that takes a `details` object with `path`, `id`, `referrers` and `message` properties. If you `throw` from this function, the build will fail
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
handleEntryGeneratorMismatch?: PrerenderEntryGeneratorMismatchHandlerValue;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"fail"`
- <span class="tag since">available since</span> v1.16.0
</div>
How to respond when an entry generated by the `entries` export doesn't match the route it was generated from.
- `'fail'` — fail the build
- `'ignore'` - silently ignore the failure and continue
- `'warn'` — continue, but print a warning
- `(details) => void` — a custom error handler that takes a `details` object with `generatedFromId`, `entry`, `matchedId` and `message` properties. If you `throw` from this function, the build will fail
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
handleUnseenRoutes?: PrerenderUnseenRoutesHandlerValue;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"fail"`
- <span class="tag since">available since</span> v2.16.0
</div>
How to respond when a route is marked as prerenderable but has not been prerendered.
- `'fail'` — fail the build
- `'ignore'` - silently ignore the failure and continue
- `'warn'` — continue, but print a warning
- `(details) => void` — a custom error handler that takes a `details` object with a `routes` property which contains all routes that haven't been prerendered. If you `throw` from this function, the build will fail
The default behavior is to fail the build. This may be undesirable when you know that some of your routes may never be reached under certain
circumstances such as a CMS not returning data for a specific area, resulting in certain routes never being reached.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
origin?: string;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"http://sveltekit-prerender"`
</div>
The value of `url.origin` during prerendering; useful if it is included in rendered content.
</div>
</div>
</div>
## router
<div class="ts-block-property-bullets">
</div>
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
type?: 'pathname' | 'hash';
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"pathname"`
- <span class="tag since">available since</span> v2.14.0
</div>
What type of client-side router to use.
- `'pathname'` is the default and means the current URL pathname determines the route
- `'hash'` means the route is determined by `location.hash`. In this case, SSR and prerendering are disabled. This is only recommended if `pathname` is not an option, for example because you don't control the webserver where your app is deployed.
It comes with some caveats: you can't use server-side rendering (or indeed any server logic), and you have to make sure that the links in your app all start with #/, or they won't work. Beyond that, everything works exactly like a normal SvelteKit app.
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
resolution?: 'client' | 'server';
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `"client"`
- <span class="tag since">available since</span> v2.17.0
</div>
How to determine which route to load when navigating to a new page.
By default, SvelteKit will serve a route manifest to the browser.
When navigating, this manifest is used (along with the `reroute` hook, if it exists) to determine which components to load and which `load` functions to run.
Because everything happens on the client, this decision can be made immediately. The drawback is that the manifest needs to be
loaded and parsed before the first navigation can happen, which may have an impact if your app contains many routes.
Alternatively, SvelteKit can determine the route on the server. This means that for every navigation to a path that has not yet been visited, the server will be asked to determine the route.
This has several advantages:
- The client does not need to load the routing manifest upfront, which can lead to faster initial page loads
- The list of routes is hidden from public view
- The server has an opportunity to intercept each navigation (for example through a middleware), enabling (for example) A/B testing opaque to SvelteKit
The drawback is that for unvisited paths, resolution will take slightly longer (though this is mitigated by [preloading](/docs/kit/link-options#data-sveltekit-preload-data)).
> [!NOTE] When using server-side route resolution and prerendering, the resolution is prerendered along with the route itself.
</div>
</div>
</div>
## serviceWorker
<div class="ts-block-property-bullets">
</div>
<div class="ts-block-property-children">
</div>
## typescript
<div class="ts-block-property-bullets">
</div>
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
config?: (config: Record<string, any>) => Record<string, any> | void;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `(config) => config`
- <span class="tag since">available since</span> v1.3.0
</div>
A function that allows you to edit the generated `tsconfig.json`. You can mutate the config (recommended) or return a new one.
This is useful for extending a shared `tsconfig.json` in a monorepo root, for example.
Note that any paths configured here should be relative to the generated config file, which is written to `.svelte-kit/tsconfig.json`.
</div>
</div>
</div>
## version
<div class="ts-block-property-bullets">
</div>
Client-side navigation can be buggy if you deploy a new version of your app while people are using it. If the code for the new page is already loaded, it may have stale content; if it isn't, the app's route manifest may point to a JavaScript file that no longer exists.
SvelteKit helps you solve this problem through version management.
If SvelteKit encounters an error while loading the page and detects that a new version has been deployed (using the `name` specified here, which defaults to a timestamp of the build) it will fall back to traditional full-page navigation.
Not all navigations will result in an error though, for example if the JavaScript for the next page is already loaded. If you still want to force a full-page navigation in these cases, use techniques such as setting the `pollInterval` and then using `beforeNavigate`:
```html
/// file: +layout.svelte
<script>
import { beforeNavigate } from '$app/navigation';
import { updated } from '$app/state';
beforeNavigate(({ willUnload, to }) => {
if (updated.current && !willUnload && to?.url) {
location.href = to.url.href;
}
});
</script>
```
If you set `pollInterval` to a non-zero value, SvelteKit will poll for new versions in the background and set the value of [`updated.current`](/docs/kit/$app-state#updated) `true` when it detects one.
<div class="ts-block-property-children">
<div class="ts-block-property">
```ts
// @noErrors
name?: string;
```
<div class="ts-block-property-details">
The current app version string. If specified, this must be deterministic (e.g. a commit ref rather than `Math.random()` or `Date.now().toString()`), otherwise defaults to a timestamp of the build.
For example, to use the current commit hash, you could do use `git rev-parse HEAD`:
```js
// @errors: 7031
/// file: svelte.config.js
import * as child_process from 'node:child_process';
export default {
kit: {
version: {
name: child_process.execSync('git rev-parse HEAD').toString().trim()
}
}
};
```
</div>
</div>
<div class="ts-block-property">
```ts
// @noErrors
pollInterval?: number;
```
<div class="ts-block-property-details">
<div class="ts-block-property-bullets">
- <span class="tag">default</span> `0`
</div>
The interval in milliseconds to poll for version changes. If this is `0`, no polling occurs.
</div>
</div>
</div>
# Command Line Interface
SvelteKit projects use [Vite](https://vitejs.dev), meaning you'll mostly use its CLI (albeit via `npm run dev/build/preview` scripts):
- `vite dev` — start a development server
- `vite build` — build a production version of your app
- `vite preview` — run the production version locally
However SvelteKit includes its own CLI for initialising your project:
## svelte-kit sync
`svelte-kit sync` creates the `tsconfig.json` and all generated types (which you can import as `./$types` inside routing files) for your project. When you create a new project, it is listed as the `prepare` script and will be run automatically as part of the npm lifecycle, so you should not ordinarily have to run this command.
# Types
## Generated types
The `RequestHandler` and `Load` types both accept a `Params` argument allowing you to type the `params` object. For example this endpoint expects `foo`, `bar` and `baz` params:
```js
/// file: src/routes/[foo]/[bar]/[baz]/+server.js
// @errors: 2355 2322 1360
/** @type {import('@sveltejs/kit').RequestHandler<{
foo: string;
bar: string;
baz: string
}>} */
export async function GET({ params }) {
// ...
}
```
Needless to say, this is cumbersome to write out, and less portable (if you were to rename the `[foo]` directory to `[qux]`, the type would no longer reflect reality).
To solve this problem, SvelteKit generates `.d.ts` files for each of your endpoints and pages:
```ts
/// file: .svelte-kit/types/src/routes/[foo]/[bar]/[baz]/$types.d.ts
/// link: true
import type * as Kit from '@sveltejs/kit';
type RouteParams = {
foo: string;
bar: string;
baz: string;
};
export type RequestHandler = Kit.RequestHandler<RouteParams>;
export type PageLoad = Kit.Load<RouteParams>;
```
These files can be imported into your endpoints and pages as siblings, thanks to the [`rootDirs`](https://www.typescriptlang.org/tsconfig#rootDirs) option in your TypeScript configuration:
```js
/// file: src/routes/[foo]/[bar]/[baz]/+server.js
// @filename: $types.d.ts
import type * as Kit from '@sveltejs/kit';
type RouteParams = {
foo: string;
bar: string;
baz: string;
}
export type RequestHandler = Kit.RequestHandler<RouteParams>;
// @filename: index.js
// @errors: 2355 2322
// ---cut---
/** @type {import('./$types').RequestHandler} */
export async function GET({ params }) {
// ...
}
```
```js
/// file: src/routes/[foo]/[bar]/[baz]/+page.js
// @filename: $types.d.ts
import type * as Kit from '@sveltejs/kit';
type RouteParams = {
foo: string;
bar: string;
baz: string;
}
export type PageLoad = Kit.Load<RouteParams>;
// @filename: index.js
// @errors: 2355
// ---cut---
/** @type {import('./$types').PageLoad} */
export async function load({ params, fetch }) {
// ...
}
```
The return types of the load functions are then available through the `$types` module as `PageData` and `LayoutData` respectively, while the union of the return values of all `Actions` is available as `ActionData`.
Starting with version 2.16.0, two additional helper types are provided: `PageProps` defines `data: PageData`, as well as `form: ActionData`, when there are actions defined, while `LayoutProps` defines `data: LayoutData`, as well as `children: Snippet`.
```svelte
<!--- file: src/routes/+page.svelte --->
<script>
/** @type {import('./$types').PageProps} */
let { data, form } = $props();
</script>
```
> [!LEGACY]
> Before 2.16.0:
> ```svelte
> <!--- file: src/routes/+page.svelte --->
> <script>
> /** @type {{ data: import('./$types').PageData, form: import('./$types').ActionData }} */
> let { data, form } = $props();
> </script>
> ```
>
> Using Svelte 4:
> ```svelte
> <!--- file: src/routes/+page.svelte --->
> <script>
> /** @type {import('./$types').PageData} */
> export let data;
> /** @type {import('./$types').ActionData} */
> export let form;
> </script>
> ```
> [!NOTE] For this to work, your own `tsconfig.json` or `jsconfig.json` should extend from the generated `.svelte-kit/tsconfig.json` (where `.svelte-kit` is your [`outDir`](configuration#outDir)):
>
> `{ "extends": "./.svelte-kit/tsconfig.json" }`
### Default tsconfig.json
The generated `.svelte-kit/tsconfig.json` file contains a mixture of options. Some are generated programmatically based on your project configuration, and should generally not be overridden without good reason:
```json
/// file: .svelte-kit/tsconfig.json
{
"compilerOptions": {
"paths": {
"$lib": ["../src/lib"],
"$lib/*": ["../src/lib/*"]
},
"rootDirs": ["..", "./types"]
},
"include": [
"ambient.d.ts",
"non-ambient.d.ts",
"./types/**/$types.d.ts",
"../vite.config.js",
"../vite.config.ts",
"../src/**/*.js",
"../src/**/*.ts",
"../src/**/*.svelte",
"../tests/**/*.js",
"../tests/**/*.ts",
"../tests/**/*.svelte"
],
"exclude": [
"../node_modules/**",
"../src/service-worker.js",
"../src/service-worker/**/*.js",
"../src/service-worker.ts",
"../src/service-worker/**/*.ts",
"../src/service-worker.d.ts",
"../src/service-worker/**/*.d.ts"
]
}
```
Others are required for SvelteKit to work properly, and should also be left untouched unless you know what you're doing:
```json
/// file: .svelte-kit/tsconfig.json
{
"compilerOptions": {
// this ensures that types are explicitly
// imported with `import type`, which is
// necessary as Svelte/Vite cannot
// otherwise compile components correctly
"verbatimModuleSyntax": true,
// Vite compiles one TypeScript module
// at a time, rather than compiling
// the entire module graph
"isolatedModules": true,
// Tell TS it's used only for type-checking
"noEmit": true,
// This ensures both `vite build`
// and `svelte-package` work correctly
"lib": ["esnext", "DOM", "DOM.Iterable"],
"moduleResolution": "bundler",
"module": "esnext",
"target": "esnext"
}
}
```
Use the [`typescript.config` setting](configuration#typescript) in `svelte.config.js` to extend or modify the generated `tsconfig.json`.
## $lib
This is a simple alias to `src/lib`. It allows you to access common components and utility modules without `../../../../` nonsense.
### $lib/server
A subdirectory of `$lib`. SvelteKit will prevent you from importing any modules in `$lib/server` into client-side code. See [server-only modules](server-only-modules).
## app.d.ts
The `app.d.ts` file is home to the ambient types of your apps, i.e. types that are available without explicitly importing them.
Always part of this file is the `App` namespace. This namespace contains several types that influence the shape of certain SvelteKit features you interact with.
## Error
Defines the common shape of expected and unexpected errors. Expected errors are thrown using the `error` function. Unexpected errors are handled by the `handleError` hooks which should return this shape.
<div class="ts-block">
```dts
interface Error {/*…*/}
```
<div class="ts-block-property">
```dts
message: string;
```
<div class="ts-block-property-details"></div>
</div></div>
## Locals
The interface that defines `event.locals`, which can be accessed in server [hooks](/docs/kit/hooks) (`handle`, and `handleError`), server-only `load` functions, and `+server.js` files.
<div class="ts-block">
```dts
interface Locals {}
```
</div>
## PageData
Defines the common shape of the [page.data state](/docs/kit/$app-state#page) and [$page.data store](/docs/kit/$app-stores#page) - that is, the data that is shared between all pages.
The `Load` and `ServerLoad` functions in `./$types` will be narrowed accordingly.
Use optional properties for data that is only present on specific pages. Do not add an index signature (`[key: string]: any`).
<div class="ts-block">
```dts
interface PageData {}
```
</div>
## PageState
The shape of the `page.state` object, which can be manipulated using the [`pushState`](/docs/kit/$app-navigation#pushState) and [`replaceState`](/docs/kit/$app-navigation#replaceState) functions from `$app/navigation`.
<div class="ts-block">
```dts
interface PageState {}
```
</div>
## Platform
If your adapter provides [platform-specific context](/docs/kit/adapters#Platform-specific-context) via `event.platform`, you can specify it here.
<div class="ts-block">
```dts
interface Platform {}
```
</div>