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@sveltejs/kit

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

Adapter

interface Adapter {
  name: string;
  adapt(builder: Builder): MaybePromise<void>;
}

Builder

interface Builder {
  log: Logger;
  rimraf(dir: string): void;
  mkdirp(dir: string): void;

  config: ValidatedConfig;
  prerendered: Prerendered;
  /**   * Create entry points that map to individual functions   * @param fn A function that groups a set of routes into an entry point   */  createEntries(fn: (route: RouteDefinition) => AdapterEntry): Promise<void>;

  generateManifest: (opts: {
    relativePath: string;
    format?: 'esm' | 'cjs';
  }) => string;

  getBuildDirectory(name: string): string;
  getClientDirectory(): string;
  getServerDirectory(): string;
  getStaticDirectory(): string;
  /**   * @param dest the destination folder to which files should be copied   * @returns an array of paths corresponding to the files that have been created by the copy   */  writeClient(dest: string): string[];
  /**   * @param dest   */  writePrerendered(
    dest: string,
    opts?: {
      fallback?: string;
    }
  ): string[];
  /**   * @param dest the destination folder to which files should be copied   * @returns an array of paths corresponding to the files that have been created by the copy   */  writeServer(dest: string): string[];
  /**   * @param from the source file or folder   * @param to the destination file or folder   * @param opts.filter a function to determine whether a file or folder should be copied   * @param opts.replace a map of strings to replace   * @returns an array of paths corresponding to the files that have been created by the copy   */  copy(
    from: string,
    to: string,
    opts?: {
      filter?: (basename: string) => boolean;
      replace?: Record<string, string>;
    }
  ): string[];
}

Config

interface Config {
  compilerOptions?: CompileOptions;
  extensions?: string[];
  kit?: KitConfig;
  preprocess?: any;
}

ExternalFetch

interface ExternalFetch {
  (req: Request): Promise<Response>;
}

GetSession

interface GetSession {
  (event: RequestEvent): MaybePromise<App.Session>;
}

Handle

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

HandleError

interface HandleError {
  (input: { error: Error & { frame?: string }; event: RequestEvent }): void;
}

KitConfig

interface KitConfig {
  adapter?: Adapter;
  alias?: Record<string, string>;
  appDir?: string;
  browser?: {
    hydrate?: boolean;
    router?: boolean;
  };
  csp?: {
    mode?: 'hash' | 'nonce' | 'auto';
    directives?: CspDirectives;
    reportOnly?: CspDirectives;
  };
  moduleExtensions?: string[];
  files?: {
    assets?: string;
    hooks?: string;
    lib?: string;
    params?: string;
    routes?: string;
    serviceWorker?: string;
    template?: string;
  };
  inlineStyleThreshold?: number;
  methodOverride?: {
    parameter?: string;
    allowed?: string[];
  };
  outDir?: string;
  package?: {
    dir?: string;
    emitTypes?: boolean;
    exports?(filepath: string): boolean;
    files?(filepath: string): boolean;
  };
  paths?: {
    assets?: string;
    base?: string;
  };
  prerender?: {
    concurrency?: number;
    crawl?: boolean;
    default?: boolean;
    enabled?: boolean;
    entries?: Array<'*' | `/${string}`>;
    onError?: PrerenderOnErrorValue;
    origin?: string;
  };
  routes?: (filepath: string) => boolean;
  serviceWorker?: {
    register?: boolean;
    files?: (filepath: string) => boolean;
  };
  trailingSlash?: TrailingSlash;
  version?: {
    name?: string;
    pollInterval?: number;
  };
}

Load

The (event: LoadEvent) => LoadOutput load function exported from <script context="module"> in a page or layout.

Note that you can use generated types instead of manually specifying the Params generic argument.

interface Load<
  Params extends Record<string, string> = Record<string, string>,
  InputProps extends Record<string, any> = Record<string, any>,
  OutputProps extends Record<string, any> = InputProps
> {
  (
    event: LoadEvent<Params, InputProps>
  ): MaybePromise<LoadOutput<OutputProps> | void>;
}

LoadEvent

interface LoadEvent<
  Params extends Record<string, string> = Record<string, string>,
  Props extends Record<string, any> = Record<string, any>
> {
  fetch(info: RequestInfo, init?: RequestInit): Promise<Response>;
  params: Params;
  props: Props;
  routeId: string | null;
  session: App.Session;
  stuff: Partial<App.Stuff>;
  url: URL;
  status: number | null;
  error: Error | null;
}

LoadOutput

interface LoadOutput<Props extends Record<string, any> = Record<string, any>> {
  status?: number;
  error?: string | Error;
  redirect?: string;
  props?: Props;
  stuff?: Partial<App.Stuff>;
  cache?: LoadOutputCache;
  dependencies?: string[];
}

LoadOutputCache

interface LoadOutputCache {
  maxage: number;
  private?: boolean;
}

Navigation

interface Navigation {
  from: URL;
  to: URL;
}

Page

interface Page<Params extends Record<string, string> = Record<string, string>> {
  url: URL;
  params: Params;
  routeId: string | null;
  stuff: App.Stuff;
  status: number;
  error: Error | null;
}

ParamMatcher

interface ParamMatcher {
  (param: string): boolean;
}

RequestEvent

interface RequestEvent<
  Params extends Record<string, string> = Record<string, string>
> {
  clientAddress: string;
  locals: App.Locals;
  params: Params;
  platform: Readonly<App.Platform>;
  request: Request;
  routeId: string | null;
  url: URL;
}

RequestHandler

A (event: RequestEvent) => RequestHandlerOutput function exported from an endpoint 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.

The next generic argument Output is used to validate the returned body from your functions by passing it through BodyValidator, which will make sure the variable in the body matches what with you assign here. It defaults to ResponseBody, which will error when body receives a custom object type.

interface RequestHandler<
  Params extends Record<string, string> = Record<string, string>,
  Output = ResponseBody
> {
  (event: RequestEvent<Params>): MaybePromise<RequestHandlerOutput<Output>>;
}

RequestHandlerOutput

interface RequestHandlerOutput<Output = ResponseBody> {
  status?: number;
  headers?: Headers | Partial<ResponseHeaders>;
  body?: Output extends ResponseBody ? Output : BodyValidator<Output>;
}

ResolveOptions

interface ResolveOptions {
  ssr?: boolean;
  transformPageChunk?: (input: {
    html: string;
    done: boolean;
  }) => MaybePromise<string | undefined>;
}

ResponseBody

type ResponseBody = JSONValue | Uint8Array | ReadableStream | Error;

SSRManifest

interface SSRManifest {
  appDir: string;
  assets: Set<string>;
  mimeTypes: Record<string, string>;
  /** private fields */  _: {
    entry: {
      file: string;
      imports: string[];
      stylesheets: string[];
    };
    nodes: SSRNodeLoader[];
    routes: SSRRoute[];
    matchers: () => Promise<Record<string, ParamMatcher>>;
  };
}

Server

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

Additional types

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

AdapterEntry

interface AdapterEntry {
  /**   * 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   */  id: string;
  /**   * A function that compares the candidate route with the current route to determine   * if it should be treated as a fallback for the current route. For example, `/foo/[c]`   * is a fallback for `/foo/a-[b]`, and `/[...catchall]` is a fallback for all routes   */  filter: (route: RouteDefinition) => boolean;
  /**   * 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.   */  complete: (entry: {
    generateManifest: (opts: {
      relativePath: string;
      format?: 'esm' | 'cjs';
    }) => string;
  }) => MaybePromise<void>;
}

BodyValidator

type BodyValidator<T> = {
  [P in keyof T]: T[P] extends { [k: string]: unknown }
    ? BodyValidator<T[P]> // recurse when T[P] is an object
    : T[P] extends BigInt | Function | Symbol
    ? never
    : T[P];
};

Csp

namespace Csp {
  type ActionSource = 'strict-dynamic' | 'report-sample';
  type BaseSource =
    | 'self'
    | 'unsafe-eval'
    | 'unsafe-hashes'
    | 'unsafe-inline'
    | '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 = `:${number}` | '' | ':*';
  type SchemeSource =
    | 'http:'
    | 'https:'
    | 'data:'
    | 'mediastream:'
    | 'blob:'
    | 'filesystem:';
  type Source = HostSource | SchemeSource | CryptoSource | BaseSource;
  type Sources = Source[];
  type UriPath = `${HttpDelineator}${string}`;
}

CspDirectives

interface CspDirectives {
  'child-src'?: Csp.Sources;
  'default-src'?: Array<Csp.Source | Csp.ActionSource>;
  'frame-src'?: Csp.Sources;
  'worker-src'?: Csp.Sources;
  'connect-src'?: Csp.Sources;
  'font-src'?: Csp.Sources;
  'img-src'?: Csp.Sources;
  'manifest-src'?: Csp.Sources;
  'media-src'?: Csp.Sources;
  'object-src'?: Csp.Sources;
  'prefetch-src'?: Csp.Sources;
  'script-src'?: Array<Csp.Source | Csp.ActionSource>;
  'script-src-elem'?: Csp.Sources;
  'script-src-attr'?: Csp.Sources;
  'style-src'?: Array<Csp.Source | Csp.ActionSource>;
  'style-src-elem'?: Csp.Sources;
  'style-src-attr'?: Csp.Sources;
  'base-uri'?: Array<Csp.Source | Csp.ActionSource>;
  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'
  >;
  'form-action'?: Array<Csp.Source | Csp.ActionSource>;
  'frame-ancestors'?: Array<
    Csp.HostSource | Csp.SchemeSource | Csp.FrameSource
  >;
  'navigate-to'?: Array<Csp.Source | Csp.ActionSource>;
  'report-uri'?: Csp.UriPath[];
  'report-to'?: string[];

  'require-trusted-types-for'?: Array<'script'>;
  'trusted-types'?: Array<'none' | 'allow-duplicates' | '*' | string>;
  'upgrade-insecure-requests'?: boolean;
  /** @deprecated */  'require-sri-for'?: Array<'script' | 'style' | 'script style'>;
  /** @deprecated */  'block-all-mixed-content'?: boolean;
  /** @deprecated */  'plugin-types'?: Array<`${string}/${string}` | 'none'>;
  /** @deprecated */  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'
  >;
}

HttpMethod

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

JSONObject

interface JSONObject {
  [key: string]: JSONValue;
}

JSONValue

type JSONValue =
  | string
  | number
  | boolean
  | null
  | undefined
  | ToJSON
  | JSONValue[]
  | JSONObject;

Logger

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

MaybePromise

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

PrerenderErrorHandler

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

PrerenderOnErrorValue

type PrerenderOnErrorValue = 'fail' | 'continue' | PrerenderErrorHandler;

Prerendered

interface Prerendered {
  pages: Map<
    string,
    {
      /** The location of the .html file relative to the output directory */      file: string;
    }
  >;
  assets: Map<
    string,
    {
      /** The MIME type of the asset */      type: string;
    }
  >;
  redirects: Map<
    string,
    {
      status: number;
      location: string;
    }
  >;
  /** An array of prerendered paths (without trailing slashes, regardless of the trailingSlash config) */  paths: string[];
}

RequestOptions

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

ResponseHeaders

string[] is only for set-cookie, everything else must be type of string

type ResponseHeaders = Record<string, string | number | string[]>;

RouteDefinition

interface RouteDefinition {
  id: string;
  type: 'page' | 'endpoint';
  pattern: RegExp;
  segments: RouteSegment[];
  methods: HttpMethod[];
}

RouteSegment

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

ToJSON

interface ToJSON {
  toJSON(...args: any[]): Exclude<JSONValue, ToJSON>;
}

TrailingSlash

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

App

It's possible to tell SvelteKit how to type objects inside your app by declaring the App namespace. By default, a new project will have a file called src/app.d.ts containing the following:

/// <reference types="@sveltejs/kit" />

declare namespace App {
  interface Locals {}

  interface Platform {}

  interface Session {}

  interface Stuff {}
}

By populating these interfaces, you will gain type safety when using event.locals, event.platform, session and stuff.

Note that since it's an ambient declaration file, you have to be careful when using import statements. Once you add an import at the top level, the declaration file is no longer considered ambient and you lose access to these typings in other files. To avoid this, either use the import(...) function:

interface Locals {
  user: import('$lib/types').User;
}

Or wrap the namespace with declare global:

import { User } from '$lib/types';

declare global {
  namespace App {
    interface Locals {
      user: User;
    }
    // ...  }
}

Locals

The interface that defines event.locals, which can be accessed in hooks (handle, handleError and getSession) and endpoints.

interface Locals {}

Platform

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

interface Platform {}

Session

The interface that defines session, both as an argument to load functions and the value of the session store.

interface Session {}

Stuff

The interface that defines stuff, as input or output to load or as the value of the stuff property of the page store.

interface Stuff {}

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].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.
  // ...
}

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]/__types/[baz].d.ts
import type { RequestHandler as GenericRequestHandler, Load as GenericLoad } from '@sveltejs/kit';

export type RequestHandler<Body = any> = GenericRequestHandler<
  { foo: string; bar: string; baz: string },
  Body
>;

export type Load<
  InputProps extends Record<string, any> = Record<string, any>,
  OutputProps extends Record<string, any> = InputProps
> = GenericLoad<{ foo: string; bar: string; baz: string }, InputProps, OutputProps>;

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].js
ts
/** @type {import('./__types/[baz]').RequestHandler} */
export async function GET({ params }) {
  // ...
}
<script context="module">
  /** @type {import('./__types/[baz]').Load} */  export async function load({ params, fetch, session, stuff }) {
    // ...  }
</script>

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
{
  "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
{
  "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-kit package` work correctly
    "lib": ["esnext", "DOM"],
    "moduleResolution": "node",
    "module": "esnext",
    "target": "esnext"
  }
}
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