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Reference

Types

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Public types

The following types can be imported from @sveltejs/kit:

Action

Shape of a form action method that is part of export const actions = {..} in +page.server.js. See form actions for more information.

ts
type Action<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends string | null = string | null
> = (
event: RequestEvent<Params, RouteId>
) => MaybePromise<OutputData>;

ActionFailure

ts
interface ActionFailure<
T extends Record<string, unknown> | undefined = undefined
> {}
ts
status: number;
ts
data: T;
ts
[uniqueSymbol]: true;

ActionResult

When calling a form action via fetch, the response will be one of these shapes.

<form method="post" use:enhance={() => {
  return ({ result }) => {
		// result is of type ActionResult
  };
}}
ts
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 };

Actions

Shape of the export const actions = {..} object in +page.server.js. See form actions for more information.

ts
type Actions<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends string | null = string | null
> = Record<string, Action<Params, OutputData, RouteId>>;

Adapter

Adapters are responsible for taking the production build and turning it into something that can be deployed to a platform of your choosing.

ts
interface Adapter {}
ts
name: string;

The name of the adapter, using for logging. Will typically correspond to the package name.

ts
adapt(builder: Builder): MaybePromise<void>;
  • builder An object provided by SvelteKit that contains methods for adapting the app

This function is called after SvelteKit has built your app.

ts
supports?: {}

Checks called during dev and build to determine whether specific features will work in production with this adapter

ts
read?: (details: { config: any; route: { id: string } }) => boolean;
  • config The merged route config

Test support for read from $app/server

ts
emulate?(): MaybePromise<Emulator>;

Creates an Emulator, which allows the adapter to influence the environment during dev, build and prerendering

AfterNavigate

The argument passed to afterNavigate callbacks.

ts
interface AfterNavigate extends Omit<Navigation, 'type'> {}
ts
type: Exclude<NavigationType, 'leave'>;

The type of navigation:

  • enter: The app has hydrated
  • form: The user submitted a <form>
  • 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
ts
willUnload: false;

Since afterNavigate callbacks are called after a navigation completes, they will never be called with a navigation that unloads the page.

AwaitedActions

ts
type AwaitedActions<
T extends Record<string, (...args: any) => any>
> = OptionalUnion<
{
[Key in keyof T]: UnpackValidationError<
Awaited<ReturnType<T[Key]>>
>;
}[keyof T]
>;

BeforeNavigate

The argument passed to beforeNavigate callbacks.

ts
interface BeforeNavigate extends Navigation {}
ts
cancel(): void;

Call this to prevent the navigation from starting.

Builder

This object is passed to the adapt function of adapters. It contains various methods and properties that are useful for adapting the app.

ts
interface Builder {}
ts
log: Logger;

Print messages to the console. log.info and log.minor are silent unless Vite's logLevel is info.

ts
rimraf(dir: string): void;

Remove dir and all its contents.

ts
mkdirp(dir: string): void;

Create dir and any required parent directories.

ts
config: ValidatedConfig;

The fully resolved svelte.config.js.

ts
prerendered: Prerendered;

Information about prerendered pages and assets, if any.

ts
routes: RouteDefinition[];

An array of all routes (including prerendered)

ts
createEntries(fn: (route: RouteDefinition) => AdapterEntry): Promise<void>;
  • fn A function that groups a set of routes into an entry point
  • deprecated Use builder.routes instead

Create separate functions that map to one or more routes of your app.

ts
findServerAssets(routes: RouteDefinition[]): string[];

Find all the assets imported by server files belonging to routes

ts
generateFallback(dest: string): Promise<void>;

Generate a fallback page for a static webserver to use when no route is matched. Useful for single-page apps.

ts
generateEnvModule(): void;

Generate a module exposing build-time environment variables as $env/dynamic/public.

ts
generateManifest(opts: { relativePath: string; routes?: RouteDefinition[] }): string;
  • opts a relative path to the base directory of the app and optionally in which format (esm or cjs) the manifest should be generated

Generate a server-side manifest to initialise the SvelteKit server with.

ts
getBuildDirectory(name: string): string;
  • name path to the file, relative to the build directory

Resolve a path to the name directory inside outDir, e.g. /path/to/.svelte-kit/my-adapter.

ts
getClientDirectory(): string;

Get the fully resolved path to the directory containing client-side assets, including the contents of your static directory.

ts
getServerDirectory(): string;

Get the fully resolved path to the directory containing server-side code.

ts
getAppPath(): string;

Get the application path including any configured base path, e.g. my-base-path/_app.

ts
writeClient(dest: string): string[];
  • dest the destination folder
  • returns an array of files written to dest

Write client assets to dest.

ts
writePrerendered(dest: string): string[];
  • dest the destination folder
  • returns an array of files written to dest

Write prerendered files to dest.

ts
writeServer(dest: string): string[];
  • dest the destination folder
  • returns an array of files written to dest

Write server-side code to dest.

ts
copy(
from: string,
to: string,
opts?: {
filter?(basename: string): boolean;
replace?: Record<string, string>;
}
): string[];
  • 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
  • returns an array of files that were copied

Copy a file or directory.

ts
compress(directory: string): Promise<void>;
  • directory The directory containing the files to be compressed

Compress files in directory with gzip and brotli, where appropriate. Generates .gz and .br files alongside the originals.

Config

ts
interface Config {}

See the configuration reference for details.

Cookies

ts
interface Cookies {}
ts
get(name: string, opts?: import('cookie').CookieParseOptions): string | undefined;
  • name the name of the cookie
  • opts the options, passed directly to cookie.parse. See documentation here

Gets a cookie that was previously set with cookies.set, or from the request headers.

ts
getAll(opts?: import('cookie').CookieParseOptions): Array<{ name: string; value: string }>;
  • opts the options, passed directly to cookie.parse. See documentation here

Gets all cookies that were previously set with cookies.set, or from the request headers.

ts
set(
name: string,
value: string,
opts: import('cookie').CookieSerializeOptions & { path: string }
): void;
  • name the name of the cookie
  • value the cookie value
  • opts the options, passed directly to cookie.serialize. See documentation here

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

ts
delete(name: string, opts: import('cookie').CookieSerializeOptions & { path: string }): void;
  • 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

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

ts
serialize(
name: string,
value: string,
opts: import('cookie').CookieSerializeOptions & { path: string }
): string;
  • name the name of the cookie
  • value the cookie value
  • opts the options, passed directly to cookie.serialize. See documentation here

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

Emulator

A collection of functions that influence the environment during dev, build and prerendering

ts
interface Emulator {}
ts
platform?(details: { config: any; prerender: PrerenderOption }): MaybePromise<App.Platform>;

A function that is called with the current route config and prerender option and returns an App.Platform object

Handle

The handle hook runs every time the SvelteKit server receives a request and determines the 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).

ts
type Handle = (input: {
event: RequestEvent;
resolve(
event: RequestEvent,
opts?: ResolveOptions
): MaybePromise<Response>;
}) => MaybePromise<Response>;

HandleClientError

The client-side 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.

ts
type HandleClientError = (input: {
error: unknown;
event: NavigationEvent;
status: number;
message: string;
}) => MaybePromise<void | App.Error>;

HandleFetch

The handleFetch hook allows you to modify (or replace) a fetch request that happens inside a load function that runs on the server (or during pre-rendering)

ts
type HandleFetch = (input: {
event: RequestEvent;
request: Request;
fetch: typeof fetch;
}) => MaybePromise<Response>;

HandleServerError

The server-side 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.

ts
type HandleServerError = (input: {
error: unknown;
event: RequestEvent;
status: number;
message: string;
}) => MaybePromise<void | App.Error>;

HttpError

The object returned by the error function.

ts
interface HttpError {}
ts
status: number;

The HTTP status code, in the range 400-599.

ts
body: App.Error;

The content of the error.

KitConfig

ts
interface KitConfig {}

See the configuration reference for details.

LessThan

ts
type LessThan<
TNumber extends number,
TArray extends any[] = []
> = TNumber extends TArray['length']
? TArray[number]
: LessThan<TNumber, [...TArray, TArray['length']]>;

Load

The generic form of PageLoad and LayoutLoad. You should import those from ./$types (see generated types) rather than using Load directly.

ts
type Load<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
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 string | null = string | null
> = (
event: LoadEvent<Params, InputData, ParentData, RouteId>
) => MaybePromise<OutputData>;

LoadEvent

The generic form of PageLoadEvent and LayoutLoadEvent. You should import those from ./$types (see generated types) rather than using LoadEvent directly.

ts
interface LoadEvent<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
Data extends Record<string, unknown> | null = Record<
string,
any
> | null,
ParentData extends Record<string, unknown> = Record<
string,
any
>,
RouteId extends string | null = string | null
> extends NavigationEvent<Params, RouteId> {}
ts
fetch: typeof fetch;

fetch is equivalent to the native fetch web API, 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
  • 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

ts
data: Data;

Contains the data returned by the route's server load function (in +layout.server.js or +page.server.js), if any.

ts
setHeaders(headers: Record<string, string>): void;

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:

src/routes/blog/+page.js
ts
export async function load({ fetch, setHeaders }) {
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
7031
7031
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
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();
}
src/routes/blog/+page.ts
ts
export async function load({ fetch, setHeaders }) {
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
7031
7031
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
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 API in a server-only load function instead.

setHeaders has no effect when a load function runs in the browser.

ts
parent(): Promise<ParentData>;

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.

ts
depends(...deps: Array<`${string}:${string}`>): void;

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() 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.

Custom identifiers have to be prefixed with one or more lowercase letters followed by a colon to conform to the URI specification.

The following example shows how to use depends to register a dependency on a custom identifier, which is invalidated after a button click, making the load function rerun.

src/routes/+page.js
ts
let count = 0;
export async function load({ depends }) {
Binding element 'depends' implicitly has an 'any' type.7031Binding element 'depends' implicitly has an 'any' type.
depends('increase:count');
return { count: count++ };
}
src/routes/+page.ts
ts
let count = 0;
export async function load({ depends }) {
Binding element 'depends' implicitly has an 'any' type.7031Binding element 'depends' implicitly has an 'any' type.
depends('increase:count');
return { count: count++ };
}
src/routes/+page.svelte
<script>
	import { invalidate } from '$app/navigation';

	export let data;

	const increase = async () => {
		await invalidate('increase:count');
	}
</script>

<p>{data.count}<p>
<button on:click={increase}>Increase Count</button>
ts
untrack<T>(fn: () => T): T;

Use this function to opt out of dependency tracking for everything that is synchronously called within the callback. Example:

src/routes/+page.server.js
ts
export async function load({ untrack, url }) {
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
7031
7031
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}
src/routes/+page.server.ts
ts
export async function load({ untrack, url }) {
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
7031
7031
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}

LoadProperties

ts
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;

Navigation

ts
interface Navigation {}
ts
from: NavigationTarget | null;

Where navigation was triggered from

ts
to: NavigationTarget | null;

Where navigation is going to/has gone to

ts
type: Exclude<NavigationType, 'enter'>;

The type of navigation:

  • form: The user submitted a <form>
  • 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
ts
willUnload: boolean;

Whether or not the navigation will result in the page being unloaded (i.e. not a client-side navigation)

ts
delta?: number;

In case of a history back/forward navigation, the number of steps to go back/forward

ts
complete: Promise<void>;

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

NavigationEvent

ts
interface NavigationEvent<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
RouteId extends string | null = string | null
> {}
ts
params: Params;

The parameters of the current page - e.g. for a route like /blog/[slug], a { slug: string } object

ts
route: {}

Info about the current route

ts
id: RouteId;

The ID of the current route - e.g. for src/routes/blog/[slug], it would be /blog/[slug]

ts
url: URL;

The URL of the current page

NavigationTarget

Information about the target of a specific navigation.

ts
interface NavigationTarget {}
ts
params: Record<string, string> | null;

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).

ts
route: { id: string | null };

Info about the target route

ts
url: URL;

The URL that is navigated to

NavigationType

  • enter: The app has hydrated
  • form: The user submitted a <form> with a GET method
  • leave: The user is leaving the app by closing the tab or using the back/forward buttons to go to a different document
  • 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
ts
type NavigationType =
| 'enter'
| 'form'
| 'leave'
| 'link'
| 'goto'
| 'popstate';

NumericRange

ts
type NumericRange<
TStart extends number,
TEnd extends number
> = Exclude<TEnd | LessThan<TEnd>, LessThan<TStart>>;

OnNavigate

The argument passed to onNavigate callbacks.

ts
interface OnNavigate extends Navigation {}
ts
type: Exclude<NavigationType, 'enter' | 'leave'>;

The type of navigation:

  • form: The user submitted a <form>
  • 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
ts
willUnload: false;

Since onNavigate callbacks are called immediately before a client-side navigation, they will never be called with a navigation that unloads the page.

Page

The shape of the $page store

ts
interface Page<
Params extends Record<string, string> = Record<
string,
string
>,
RouteId extends string | null = string | null
> {}
ts
url: URL;

The URL of the current page

ts
params: Params;

The parameters of the current page - e.g. for a route like /blog/[slug], a { slug: string } object

ts
route: {}

Info about the current route

ts
id: RouteId;

The ID of the current route - e.g. for src/routes/blog/[slug], it would be /blog/[slug]

ts
status: number;

Http status code of the current page

ts
error: App.Error | null;

The error object of the current page, if any. Filled from the handleError hooks.

ts
data: App.PageData & Record<string, any>;

The merged result of all data from all load functions on the current page. You can type a common denominator through App.PageData.

ts
state: App.PageState;

The page state, which can be manipulated using the pushState and replaceState functions from $app/navigation.

ts
form: any;

Filled only after a form submission. See form actions for more info.

ParamMatcher

The shape of a param matcher. See matching for more info.

ts
type ParamMatcher = (param: string) => boolean;

PrerenderOption

ts
type PrerenderOption = boolean | 'auto';

Redirect

The object returned by the redirect function

ts
interface Redirect {}
ts
status: 300 | 301 | 302 | 303 | 304 | 305 | 306 | 307 | 308;

The HTTP status code, in the range 300-308.

ts
location: string;

The location to redirect to.

RequestEvent

ts
interface RequestEvent<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
RouteId extends string | null = string | null
> {}
ts
cookies: Cookies;

Get or set cookies related to the current request

ts
fetch: typeof fetch;

fetch is equivalent to the native fetch web API, 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
  • 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

ts
getClientAddress(): string;

The client's IP address, set by the adapter.

ts
locals: App.Locals;

Contains custom data that was added to the request within the handle hook.

ts
params: Params;

The parameters of the current route - e.g. for a route like /blog/[slug], a { slug: string } object

ts
platform: Readonly<App.Platform> | undefined;

Additional data made available through the adapter.

ts
request: Request;

The original request object

ts
route: {}

Info about the current route

ts
id: RouteId;

The ID of the current route - e.g. for src/routes/blog/[slug], it would be /blog/[slug]

ts
setHeaders(headers: Record<string, string>): void;

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:

src/routes/blog/+page.js
ts
export async function load({ fetch, setHeaders }) {
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
7031
7031
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
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();
}
src/routes/blog/+page.ts
ts
export async function load({ fetch, setHeaders }) {
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
7031
7031
Binding element 'fetch' implicitly has an 'any' type.
Binding element 'setHeaders' implicitly has an 'any' type.
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 API instead.

ts
url: URL;

The requested URL.

ts
isDataRequest: boolean;

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.

ts
isSubRequest: boolean;

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.

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 instead.

ts
type RequestHandler<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
RouteId extends string | null = string | null
> = (
event: RequestEvent<Params, RouteId>
) => MaybePromise<Response>;

Reroute

The reroute hook allows you to modify the URL before it is used to determine which route to render.

ts
type Reroute = (event: { url: URL }) => void | string;

ResolveOptions

ts
interface ResolveOptions {}
ts
transformPageChunk?(input: { html: string; done: boolean }): MaybePromise<string | undefined>;
  • input the html chunk and the info if this is the last chunk

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.

ts
filterSerializedResponseHeaders?(name: string, value: string): boolean;
  • name header name
  • value header value

Determines which headers should be included in serialized responses when a load function loads a resource with fetch. By default, none will be included.

ts
preload?(input: { type: 'font' | 'css' | 'js' | 'asset'; path: string }): boolean;
  • input the type of the file and its path

Determines what should be added to the <head> tag to preload it. By default, js and css files will be preloaded.

RouteDefinition

ts
interface RouteDefinition<Config = any> {}
ts
id: string;
ts
api: {
methods: Array<HttpMethod | '*'>;
};
ts
page: {
methods: Array<Extract<HttpMethod, 'GET' | 'POST'>>;
};
ts
pattern: RegExp;
ts
prerender: PrerenderOption;
ts
segments: RouteSegment[];
ts
methods: Array<HttpMethod | '*'>;
ts
config: Config;

SSRManifest

ts
interface SSRManifest {}
ts
appDir: string;
ts
appPath: string;
ts
assets: Set<string>;
ts
mimeTypes: Record<string, string>;
ts
_: {}

private fields

ts
client: NonNullable<BuildData['client']>;
ts
nodes: SSRNodeLoader[];
ts
routes: SSRRoute[];
ts
matchers(): Promise<Record<string, ParamMatcher>>;
ts
server_assets: Record<string, number>;

A [file]: size map of all assets imported by server code

Server

ts
class Server {}
ts
constructor(manifest: SSRManifest);
ts
init(options: ServerInitOptions): Promise<void>;
ts
respond(request: Request, options: RequestOptions): Promise<Response>;

ServerInitOptions

ts
interface ServerInitOptions {}
ts
env: Record<string, string>;

A map of environment variables

ts
read?: (file: string) => ReadableStream;

A function that turns an asset filename into a ReadableStream. Required for the read export from $app/server to work

ServerLoad

The generic form of PageServerLoad and LayoutServerLoad. You should import those from ./$types (see generated types) rather than using ServerLoad directly.

ts
type ServerLoad<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
ParentData extends Record<string, any> = Record<
string,
any
>,
OutputData extends Record<string, any> | void = Record<
string,
any
> | void,
RouteId extends string | null = string | null
> = (
event: ServerLoadEvent<Params, ParentData, RouteId>
) => MaybePromise<OutputData>;

ServerLoadEvent

ts
interface ServerLoadEvent<
Params extends Partial<Record<string, string>> = Partial<
Record<string, string>
>,
ParentData extends Record<string, any> = Record<
string,
any
>,
RouteId extends string | null = string | null
> extends RequestEvent<Params, RouteId> {}
ts
parent(): Promise<ParentData>;

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.

ts
depends(...deps: string[]): void;

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() 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.

Custom identifiers have to be prefixed with one or more lowercase letters followed by a colon to conform to the URI specification.

The following example shows how to use depends to register a dependency on a custom identifier, which is invalidated after a button click, making the load function rerun.

src/routes/+page.js
ts
let count = 0;
export async function load({ depends }) {
Binding element 'depends' implicitly has an 'any' type.7031Binding element 'depends' implicitly has an 'any' type.
depends('increase:count');
return { count: count++ };
}
src/routes/+page.ts
ts
let count = 0;
export async function load({ depends }) {
Binding element 'depends' implicitly has an 'any' type.7031Binding element 'depends' implicitly has an 'any' type.
depends('increase:count');
return { count: count++ };
}
src/routes/+page.svelte
<script>
	import { invalidate } from '$app/navigation';

	export let data;

	const increase = async () => {
		await invalidate('increase:count');
	}
</script>

<p>{data.count}<p>
<button on:click={increase}>Increase Count</button>
ts
untrack<T>(fn: () => T): T;

Use this function to opt out of dependency tracking for everything that is synchronously called within the callback. Example:

src/routes/+page.js
ts
export async function load({ untrack, url }) {
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
7031
7031
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}
src/routes/+page.ts
ts
export async function load({ untrack, url }) {
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
7031
7031
Binding element 'untrack' implicitly has an 'any' type.
Binding element 'url' implicitly has an 'any' type.
// Untrack url.pathname so that path changes don't trigger a rerun
if (untrack(() => url.pathname === '/')) {
return { message: 'Welcome!' };
}
}

Snapshot

The type of export const snapshot exported from a page or layout component.

ts
interface Snapshot<T = any> {}
ts
capture: () => T;
ts
restore: (snapshot: T) => void;

SubmitFunction

ts
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>;
}) => void)
>;

Private types

The following are referenced by the public types documented above, but cannot be imported directly:

AdapterEntry

ts
interface AdapterEntry {}
ts
id: string;

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

ts
filter(route: RouteDefinition): boolean;

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
ts
complete(entry: { generateManifest(opts: { relativePath: string }): string }): MaybePromise<void>;

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.

Csp

ts
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[];
}

CspDirectives

ts
interface CspDirectives {}
ts
'child-src'?: Csp.Sources;
ts
'default-src'?: Array<Csp.Source | Csp.ActionSource>;
ts
'frame-src'?: Csp.Sources;
ts
'worker-src'?: Csp.Sources;
ts
'connect-src'?: Csp.Sources;
ts
'font-src'?: Csp.Sources;
ts
'img-src'?: Csp.Sources;
ts
'manifest-src'?: Csp.Sources;
ts
'media-src'?: Csp.Sources;
ts
'object-src'?: Csp.Sources;
ts
'prefetch-src'?: Csp.Sources;
ts
'script-src'?: Array<Csp.Source | Csp.ActionSource>;
ts
'script-src-elem'?: Csp.Sources;
ts
'script-src-attr'?: Csp.Sources;
ts
'style-src'?: Array<Csp.Source | Csp.ActionSource>;
ts
'style-src-elem'?: Csp.Sources;
ts
'style-src-attr'?: Csp.Sources;
ts
'base-uri'?: Array<Csp.Source | Csp.ActionSource>;
ts
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'
>;
ts
'form-action'?: Array<Csp.Source | Csp.ActionSource>;
ts
'frame-ancestors'?: Array<Csp.HostSource | Csp.SchemeSource | Csp.FrameSource>;
ts
'navigate-to'?: Array<Csp.Source | Csp.ActionSource>;
ts
'report-uri'?: string[];
ts
'report-to'?: string[];
ts
'require-trusted-types-for'?: Array<'script'>;
ts
'trusted-types'?: Array<'none' | 'allow-duplicates' | '*' | string>;
ts
'upgrade-insecure-requests'?: boolean;
ts
'require-sri-for'?: Array<'script' | 'style' | 'script style'>;
  • deprecated undefined
ts
'block-all-mixed-content'?: boolean;
  • deprecated undefined
ts
'plugin-types'?: Array<`${string}/${string}` | 'none'>;
  • deprecated undefined
ts
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'
>;
  • deprecated undefined

HttpMethod

ts
type HttpMethod =
| 'GET'
| 'HEAD'
| 'POST'
| 'PUT'
| 'DELETE'
| 'PATCH'
| 'OPTIONS';

Logger

ts
interface Logger {}
ts
(msg: string): void;
ts
success(msg: string): void;
ts
error(msg: string): void;
ts
warn(msg: string): void;
ts
minor(msg: string): void;
ts
info(msg: string): void;

MaybePromise

ts
type MaybePromise<T> = T | Promise<T>;

PrerenderEntryGeneratorMismatchHandler

ts
interface PrerenderEntryGeneratorMismatchHandler {}
ts
(details: { generatedFromId: string; entry: string; matchedId: string; message: string }): void;

PrerenderEntryGeneratorMismatchHandlerValue

ts
type PrerenderEntryGeneratorMismatchHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderEntryGeneratorMismatchHandler;

PrerenderHttpErrorHandler

ts
interface PrerenderHttpErrorHandler {}
ts
(details: {
status: number;
path: string;
referrer: string | null;
referenceType: 'linked' | 'fetched';
message: string;
}): void;

PrerenderHttpErrorHandlerValue

ts
type PrerenderHttpErrorHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderHttpErrorHandler;

PrerenderMap

ts
type PrerenderMap = Map<string, PrerenderOption>;

PrerenderMissingIdHandler

ts
interface PrerenderMissingIdHandler {}
ts
(details: { path: string; id: string; referrers: string[]; message: string }): void;

PrerenderMissingIdHandlerValue

ts
type PrerenderMissingIdHandlerValue =
| 'fail'
| 'warn'
| 'ignore'
| PrerenderMissingIdHandler;

PrerenderOption

ts
type PrerenderOption = boolean | 'auto';

Prerendered

ts
interface Prerendered {}
ts
pages: Map<
string,
{
/** The location of the .html file relative to the output directory */
file: string;
}
>;

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.

ts
assets: Map<
string,
{
/** The MIME type of the asset */
type: string;
}
>;

A map of path to { type } objects.

ts
redirects: Map<
string,
{
status: number;
location: string;
}
>;

A map of redirects encountered during prerendering.

ts
paths: string[];

An array of prerendered paths (without trailing slashes, regardless of the trailingSlash config)

RequestOptions

ts
interface RequestOptions {}
ts
getClientAddress(): string;
ts
platform?: App.Platform;

RouteSegment

ts
interface RouteSegment {}
ts
content: string;
ts
dynamic: boolean;
ts
rest: boolean;

TrailingSlash

ts
type TrailingSlash = 'never' | 'always' | 'ignore';

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:

src/routes/[foo]/[bar]/[baz]/+page.server.js
ts
/** @type {import('@sveltejs/kit').RequestHandler<{
foo: string;
bar: string;
baz: string
}>} */
export async function GET({ params }) {
A function whose declared type is neither 'void' nor 'any' must return a value.2355A function whose declared type is neither 'void' nor 'any' must return a value.
// ...
}
src/routes/[foo]/[bar]/[baz]/+page.server.ts
ts
export const GET: import('@sveltejs/kit').RequestHandler<{
Type '({ params }: RequestEvent<{ foo: string; bar: string; baz: string; }, string | null>) => Promise<void>' is not assignable to type 'RequestHandler<{ foo: string; bar: string; baz: string; }, string | null>'. Type 'Promise<void>' is not assignable to type 'MaybePromise<Response>'. Type 'Promise<void>' is not assignable to type 'Promise<Response>'. Type 'void' is not assignable to type 'Response'.2322Type '({ params }: RequestEvent<{ foo: string; bar: string; baz: string; }, string | null>) => Promise<void>' is not assignable to type 'RequestHandler<{ foo: string; bar: string; baz: string; }, string | null>'. Type 'Promise<void>' is not assignable to type 'MaybePromise<Response>'. Type 'Promise<void>' is not assignable to type 'Promise<Response>'. Type 'void' is not assignable to type 'Response'.
foo: string;
bar: string;
baz: string;
}> = async ({ 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:

.svelte-kit/types/src/routes/[foo]/[bar]/[baz]/$types.d.ts
ts
import type * as Kit from '@sveltejs/kit';
type RouteParams = {
foo: string;
bar: string;
baz: string;
}
export type PageServerLoad = Kit.ServerLoad<RouteParams>;
export type PageLoad = Kit.Load<RouteParams>;

These files can be imported into your endpoints and pages as siblings, thanks to the rootDirs option in your TypeScript configuration:

src/routes/[foo]/[bar]/[baz]/+page.server.js
ts
/** @type {import('./$types').PageServerLoad} */
export async function GET({ params }) {
// ...
}
src/routes/[foo]/[bar]/[baz]/+page.server.ts
ts
import type { PageServerLoad } from './$types';
export const GET: PageServerLoad = async ({ params }) => {
// ...
};
src/routes/[foo]/[bar]/[baz]/+page.js
ts
/** @type {import('./$types').PageLoad} */
export async function load({ params, fetch }) {
// ...
}
src/routes/[foo]/[bar]/[baz]/+page.ts
ts
import type { PageLoad } from './$types';
export const load: PageLoad = async ({ params, fetch }) => {
// ...
};

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):

{ "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:

.svelte-kit/tsconfig.json
ts
{
"compilerOptions": {
"baseUrl": "..",
"paths": {
"$lib": "src/lib",
"$lib/*": "src/lib/*"
},
"rootDirs": ["..", "./types"]
},
"include": ["../src/**/*.js", "../src/**/*.ts", "../src/**/*.svelte"],
"exclude": ["../node_modules/**", "./**"]
}

Others are required for SvelteKit to work properly, and should also be left untouched unless you know what you're doing:

.svelte-kit/tsconfig.json
ts
{
"compilerOptions": {
// this ensures that types are explicitly
// imported with `import type`, which is
// necessary as svelte-preprocess cannot
// otherwise compile components correctly
"importsNotUsedAsValues": "error",
// Vite compiles one TypeScript module
// at a time, rather than compiling
// the entire module graph
"isolatedModules": true,
// TypeScript cannot 'see' when you
// use an imported value in your
// markup, so we need this
"preserveValueImports": true,
// This ensures both `vite build`
// and `svelte-package` work correctly
"lib": ["esnext", "DOM", "DOM.Iterable"],
"moduleResolution": "node",
"module": "esnext",
"target": "esnext"
}
}

App

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.

ts
interface Error {}
ts
message: string;

Locals

The interface that defines event.locals, which can be accessed in hooks (handle, and handleError), server-only load functions, and +server.js files.

ts
interface Locals {}

PageData

Defines the common shape of the $page.data store - that is, the data that is shared between all pages. The Load and ServerLoad functions in ./$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).

ts
interface PageData {}

PageState

The shape of the $page.state object, which can be manipulated using the pushState and replaceState functions from $app/navigation.

ts
interface PageState {}

Platform

If your adapter provides platform-specific context via event.platform, you can specify it here.

ts
interface Platform {}