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$app/forms

import { enhance, applyAction } from '$app/forms';

SubmitFunction

type SubmitFunction<
  Success extends Record<string, unknown> | undefined = Record<string, any>,
  Invalid extends Record<string, unknown> | undefined = Record<string, any>
> = (input: {
  action: URL;
  data: FormData;
  form: HTMLFormElement;
  controller: AbortController;
  cancel: () => void;
}) =>
  | void
  | ((opts: {
      form: HTMLFormElement;
      action: URL;
      result: ActionResult<Success, Invalid>;
    }) => void);

@sveltejs/kit

The following can be imported from @sveltejs/kit:

Action

interface Action<
  Params extends Partial<Record<string, string>> = Partial<
    Record<string, string>
  >,
  OutputData extends Record<string, any> | void = Record<string, any> | void
> {
  (event: RequestEvent<Params>): MaybePromise<OutputData>;
}

ActionResult

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

type ActionResult<
  Success extends Record<string, unknown> | undefined = Record<string, any>,
  Invalid extends Record<string, unknown> | undefined = Record<string, any>
> =
  | { type: 'success'; status: number; data?: Success }
  | { type: 'invalid'; status: number; data?: Invalid }
  | { type: 'redirect'; status: number; location: string }
  | { type: 'error'; error: any };

Actions

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

Adapter

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

AwaitedActions

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

AwaitedProperties

type AwaitedProperties<input extends Record<string, any> | void> =
  AwaitedPropertiesUnion<input> extends Record<string, any>
    ? OptionalUnion<AwaitedPropertiesUnion<input>>
    : AwaitedPropertiesUnion<input>;

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[];
  /**   * @param {string} directory Path to the directory containing the files to be compressed   */  compress(directory: string): Promise<void>;
}

Config

interface Config {
  compilerOptions?: CompileOptions;
  extensions?: string[];
  kit?: KitConfig;
  package?: {
    source?: string;
    dir?: string;
    emitTypes?: boolean;
    exports?: (filepath: string) => boolean;
    files?: (filepath: string) => boolean;
  };
  preprocess?: any;
  [key: string]: any;
}

Cookies

interface Cookies {
  /**   * Gets a cookie that was previously set with `cookies.set`, or from the request headers.   */  get(
    name: string,
    opts?: import('cookie').CookieParseOptions
  ): string | undefined;
  /**   * Sets a cookie. This will add a `set-cookie` header to the response, but also make the cookie available via `cookies.get` during the current request.   *   * The `httpOnly` and `secure` options are `true` by default, 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`.   *   * By default, the `path` of a cookie is the 'directory' of the current pathname. In most cases you should explicitly set `path: '/'` to make the cookie available throughout your app.   */  set(
    name: string,
    value: string,
    opts?: import('cookie').CookieSerializeOptions
  ): void;
  /**   * Deletes a cookie by setting its value to an empty string and setting the expiry date in the past.   */  delete(name: string, opts?: import('cookie').CookieSerializeOptions): void;
  /**   * Serialize a cookie name-value pair into a Set-Cookie header string.   *   * The `httpOnly` and `secure` options are `true` by default, 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`.   *   * By default, the `path` of a cookie is the current pathname. In most cases you should explicitly set `path: '/'` to make the cookie available throughout your app.   *   * @param name the name for the cookie   * @param value value to set the cookie to   * @param options object containing serialization options   */  serialize(
    name: string,
    value: string,
    opts?: import('cookie').CookieSerializeOptions
  ): string;
}

Handle

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

HandleClientError

interface HandleClientError {
  (input: { error: unknown; event: NavigationEvent }): void | App.Error;
}

HandleFetch

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

HandleServerError

interface HandleServerError {
  (input: { error: unknown; event: RequestEvent }): void | App.Error;
}

KitConfig

interface KitConfig {
  adapter?: Adapter;
  alias?: Record<string, string>;
  appDir?: string;
  csp?: {
    mode?: 'hash' | 'nonce' | 'auto';
    directives?: CspDirectives;
    reportOnly?: CspDirectives;
  };
  csrf?: {
    checkOrigin?: boolean;
  };
  env?: {
    dir?: string;
    publicPrefix?: string;
  };
  moduleExtensions?: string[];
  files?: {
    assets?: string;
    hooks?: {
      client?: string;
      server?: string;
    };
    lib?: string;
    params?: string;
    routes?: string;
    serviceWorker?: string;
    appTemplate?: string;
    errorTemplate?: string;
  };
  inlineStyleThreshold?: number;
  outDir?: string;
  paths?: {
    assets?: string;
    base?: string;
  };
  prerender?: {
    concurrency?: number;
    crawl?: boolean;
    default?: boolean;
    enabled?: boolean;
    entries?: Array<'*' | `/${string}`>;
    onError?: PrerenderOnErrorValue;
    origin?: string;
  };
  serviceWorker?: {
    register?: boolean;
    files?: (filepath: string) => boolean;
  };
  trailingSlash?: TrailingSlash;
  version?: {
    name?: string;
    pollInterval?: number;
  };
}

Load

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

interface 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
> {
  (event: LoadEvent<Params, InputData, ParentData>): MaybePromise<OutputData>;
}

LoadEvent

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>
> extends NavigationEvent<Params> {
  fetch: typeof fetch;
  data: Data;
  setHeaders: (headers: Record<string, string>) => void;
  parent: () => Promise<ParentData>;
  depends: (...deps: string[]) => void;
}

Navigation

interface Navigation {
  from: NavigationTarget | null;
  to: NavigationTarget | null;
  type: NavigationType;
  delta?: number;
}

NavigationEvent

interface NavigationEvent<
  Params extends Partial<Record<string, string>> = Partial<
    Record<string, string>
  >
> {
  params: Params;
  routeId: string | null;
  url: URL;
}

NavigationTarget

interface NavigationTarget {
  params: Record<string, string> | null;
  routeId: string | null;
  url: URL;
}

NavigationType

type NavigationType = 'load' | 'unload' | 'link' | 'goto' | 'popstate';

Page

interface Page<Params extends Record<string, string> = Record<string, string>> {
  url: URL;
  params: Params;
  routeId: string | null;
  status: number;
  error: App.Error | null;
  data: App.PageData & Record<string, any>;
  form: any;
}

ParamMatcher

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

RequestEvent

interface RequestEvent<
  Params extends Partial<Record<string, string>> = Partial<
    Record<string, string>
  >
> {
  cookies: Cookies;
  getClientAddress: () => string;
  locals: App.Locals;
  params: Params;
  platform: Readonly<App.Platform>;
  request: Request;
  routeId: string | null;
  setHeaders: (headers: Record<string, string>) => void;
  url: URL;
}

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.

interface RequestHandler<
  Params extends Partial<Record<string, string>> = Partial<
    Record<string, string>
  >
> {
  (event: RequestEvent<Params>): MaybePromise<Response>;
}

ResolveOptions

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

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);
  init(options: ServerInitOptions): Promise<void>;
  respond(request: Request, options: RequestOptions): Promise<Response>;
}

ServerInitOptions

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

ServerLoad

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

interface 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
> {
  (event: ServerLoadEvent<Params, ParentData>): MaybePromise<OutputData>;
}

ServerLoadEvent

interface ServerLoadEvent<
  Params extends Partial<Record<string, string>> = Partial<
    Record<string, string>
  >,
  ParentData extends Record<string, any> = Record<string, any>
> extends RequestEvent<Params> {
  parent: () => Promise<ParentData>;
  depends: (...deps: string[]) => void;
}

ValidationError

interface ValidationError<
  T extends Record<string, unknown> | undefined = undefined
> extends UniqueInterface {
  status: number;
  data: T;
}

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>;
}

Csp

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 = `:${number}` | '' | ':*';
  type SchemeSource =
    | 'http:'
    | 'https:'
    | 'data:'
    | 'mediastream:'
    | 'blob:'
    | 'filesystem:';
  type Source = HostSource | SchemeSource | CryptoSource | BaseSource;
  type Sources = Source[];
  type UriPath = `${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';

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;
}

PrerenderMap

type PrerenderMap = Map<string, PrerenderOption>;

PrerenderOnErrorValue

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

PrerenderOption

type PrerenderOption = boolean | 'auto';

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;
}

RouteDefinition

interface RouteDefinition {
  id: string;
  pattern: RegExp;
  segments: RouteSegment[];
  methods: HttpMethod[];
}

RouteSegment

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

TrailingSlash

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

UniqueInterface

interface UniqueInterface {
  readonly [uniqueSymbol]: unknown;
}

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 PageData {}

  interface Platform {}
}

By populating these interfaces, you will gain type safety when using event.locals, event.platform, and data from load functions.

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;
    }
    // ...  }
}

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.

interface Error {
  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.

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).

interface PageData {}

Platform

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

interface Platform {}

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.
  // ...
}

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
import type * as Kit from '@sveltejs/kit';

interface 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('./$types').PageServerLoad} */
export async function GET({ params }) {
  // ...
}
src/routes/[foo]/[bar]/[baz]/+page.js
ts
/** @type {import('./$types').PageLoad} */
export async function load({ 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
{
  "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-package` work correctly
    "lib": ["esnext", "DOM", "DOM.Iterable"],
    "moduleResolution": "node",
    "module": "esnext",
    "target": "esnext"
  }
}
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