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Web standards

このドキュメントを通じて、SvelteKit の土台となっている標準の Web API を参照することができます。私たちは車輪の再発明をするのではなく、プラットフォームを使用します 。つまり、既存の Web 開発スキルが SvelteKit にも活用できるということです。逆に言えば、SvelteKit の学習に時間を割くことは、あなたが他の場所でも通用する良い Web 開発者になるのに役立つでしょう。

これらの API は、全てのモダンブラウザはもちろん、Cloudflare Workers、Deno、Vercel Edge Functions といったブラウザ以外の環境でも使用することができます。開発中や、(AWS Lambda を含む) Node ベースの環境向けの adapters では、必要に応じて polyfill で利用できるようにしています (現時点においては。Node は急速により多くの Web 標準のサポートを追加しています)。

具体的には、以下のことが楽にできるでしょう:

Fetch APIs

SvelteKit は、ネットワーク越しにデータを取得するために fetch を使用します。ブラウザだけでなく、hooks や サーバールート(server routes) の中でも使用することができます。

load 関数、server hooks、API routes の中では特別なバージョンの fetch を使用することができ、サーバーサイドレンダリング中に、HTTP をコールすることなく、クレデンシャルを保持したまま、直接エンドポイント(endpoints)を呼び出すことができます。(load の外側のサーバーサイドコードでクレデンシャル付きの fetch を行う場合は、明示的に cookie や authorization ヘッダーなどを渡さなければなりません。) また、通常のサーバーサイドの fetch では絶対パスの URL が必要となりますが、特別なバージョンの fetch では相対パスのリクエストが可能です。

fetch 自体の他に、Fetch API には以下のインターフェイスが含まれています:

Request

Request のインスタンスは hooks や サーバールート(server routes) で event.request という形でアクセスすることができます。これには request.json() や request.formData() など、エンドポイントに送られたデータを取得するための便利なメソッドが含まれています。

Response

Response のインスタンスは await fetch(...) と +server.js ファイル内のハンドラーから返されます。本質的には、SvelteKit アプリは Request を Response に変換するマシンです。

Headers

Headers インターフェイスでは、受け取った request.headers を読み取り、送信する response.headers をセットすることができます。例えば以下のように、request.headers を取得して、json という便利な関数を使用して response.headers を変更し送信することができます:

src/routes/what-is-my-user-agent/+server
import { function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json } from '@sveltejs/kit';

/** @type {import('./$types').RequestHandler} */
export function 
function GET({ request }: {
    request: any;
}): Response
@type{import('./$types').RequestHandler}
GET({ request: anyrequest }) {
	// log all headers
	var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.


The module exports two specific components:


    

  • A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
    • 

  • A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without calling require('console').
    • 



Warning: The global console object’s methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.


Example using the global console:


console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:


const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesource
console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).


const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.


@sincev0.1.100
log(...request: anyrequest.headers);

	// create a JSON Response using a header we received
	return function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json({
		// retrieve a specific header
		userAgent: anyuserAgent: request: anyrequest.headers.get('user-agent')
	}, {
		// set a header on the response
		ResponseInit.headers?: HeadersInit | undefinedheaders: { 'x-custom-header': 'potato' }
	});
}
import { function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json } from '@sveltejs/kit';
import type { 
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
RequestHandler } from './$types';

export const const GET: RequestHandlerGET: 
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
RequestHandler = ({ request: Request
The original request object


request }) => {
	// log all headers
	var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.


The module exports two specific components:


    

  • A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
    • 

  • A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without calling require('console').
    • 



Warning: The global console object’s methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.


Example using the global console:


console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:


const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesource
console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).


const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.


@sincev0.1.100
log(...request: Request
The original request object


request.Request.headers: Headers
Returns a Headers object consisting of the headers associated with request. Note that headers added in the network layer by the user agent will not be accounted for in this object, e.g., the “Host” header.


MDN Reference


headers);

	// create a JSON Response using a header we received
	return function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json({
		// retrieve a specific header
		userAgent: string | nulluserAgent: request: Request
The original request object


request.Request.headers: Headers
Returns a Headers object consisting of the headers associated with request. Note that headers added in the network layer by the user agent will not be accounted for in this object, e.g., the “Host” header.


MDN Reference


headers.Headers.get(name: string): string | null
MDN Reference


get('user-agent')
	}, {
		// set a header on the response
		ResponseInit.headers?: HeadersInit | undefinedheaders: { 'x-custom-header': 'potato' }
	});
};

FormData

HTML のネイティブのフォーム送信を扱う場合は、FormData オブジェクトを使用します。

src/routes/hello/+server
import { function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json } from '@sveltejs/kit';

/** @type {import('./$types').RequestHandler} */
export async function function POST(event: any): Promise<Response>
@type{import('./$types').RequestHandler}
POST(event: anyevent) {
	const const body: anybody = await event: anyevent.request.formData();

	// log all fields
	var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.


The module exports two specific components:


    

  • A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
    • 

  • A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without calling require('console').
    • 



Warning: The global console object’s methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.


Example using the global console:


console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:


const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesource
console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).


const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.


@sincev0.1.100
log([...const body: anybody]);

	return function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json({
		// get a specific field's value
		name: anyname: const body: anybody.get('name') ?? 'world'
	});
}
import { function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json } from '@sveltejs/kit';
import type { 
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
RequestHandler } from './$types';

export const const POST: RequestHandlerPOST: 
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
type RequestHandler = (event: Kit.RequestEvent<Record<string, any>, string | null>) => MaybePromise<Response>
RequestHandler = async (event: Kit.RequestEvent<Record<string, any>, string | null>event) => {
	const const body: FormDatabody = await event: Kit.RequestEvent<Record<string, any>, string | null>event.RequestEvent<Record<string, any>, string | null>.request: Request
The original request object


request.Body.formData(): Promise<FormData>
MDN Reference


formData();

	// log all fields
	var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.


The module exports two specific components:


    

  • A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
    • 

  • A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without calling require('console').
    • 



Warning: The global console object’s methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.


Example using the global console:


console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:


const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesource
console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).


const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.


@sincev0.1.100
log([...const body: FormDatabody]);

	return function json(data: any, init?: ResponseInit | undefined): Response
Create a JSON Response object from the supplied data.


@paramdata The value that will be serialized as JSON.
@paraminit Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
json({
		// get a specific field's value
		name: FormDataEntryValuename: const body: FormDatabody.FormData.get(name: string): FormDataEntryValue | null
MDN Reference


get('name') ?? 'world'
	});
};

Stream APIs

ほとんどの場合、エンドポイント(endpoints) は 上記の userAgent の例のように、完全なデータを返します。たまに、1度ではメモリに収まらない大きすぎるレスポンスを返したり、チャンクで配信したりしなければならないことがあります。このような場合のために、プラットフォームは streams — ReadableStream、WritableStream、TransformStream を提供しています。

URL APIs

URL は URL インターフェイスで表現され、origin や pathname のような便利なプロパティが含まれています (ブラウザでは hash なども)。このインターフェイスは、hooks と サーバールート(server routes) では event.url、ページ(pages) では $page.url、beforeNavigate と afterNavigate では from と to、など、様々な場所で使われています。

URLSearchParams

URL が存在する場所であれば、URLSearchParams のインスタンスである url.searchParams を使用してクエリパラメータにアクセスできます:

const const foo: string | nullfoo = const url: URLurl.URL.searchParams: URLSearchParams
MDN Reference


searchParams.URLSearchParams.get(name: string): string | null
Returns the first value associated to the given search parameter.


MDN Reference


get('foo');

Web Crypto

Web Crypto API を、グローバルの crypto 経由で使用することができます。内部では Content Security Policy ヘッダーで使用されていますが、例えば UUID を生成するのにもお使い頂けます。

const const uuid: `${string}-${string}-${string}-${string}-${string}`uuid = var crypto: Crypto
MDN Reference


crypto.Crypto.randomUUID(): `${string}-${string}-${string}-${string}-${string}`
Available only in secure contexts.


MDN Reference


randomUUID();

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