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服务工作者

服务工作者充当代理服务器,处理应用内的网络请求。这使得你的应用可以离线工作,但即使你不需要离线支持(或者由于你正在构建的应用类型而无法实际实现它),通常也值得使用服务工作者通过预先缓存你构建的 JS 和 CSS 来加快导航速度。

¥Service workers act as proxy servers that handle network requests inside your app. This makes it possible to make your app work offline, but even if you don’t need offline support (or can’t realistically implement it because of the type of app you’re building), it’s often worth using service workers to speed up navigation by precaching your built JS and CSS.

在 SvelteKit 中,如果你有 src/service-worker.js 文件(或 src/service-worker/index.js),它将被打包并自动注册。如果需要,你可以更改 服务工作者的位置

¥In SvelteKit, if you have a src/service-worker.js file (or src/service-worker/index.js) it will be bundled and automatically registered. You can change the location of your service worker if you need to.

如果你需要使用自己的逻辑注册服务工作线程或使用其他解决方案,则可以 禁用自动注册。默认注册如下所示:

¥You can disable automatic registration if you need to register the service worker with your own logic or use another solution. The default registration looks something like this:

if ('serviceWorker' in var navigator: Navigatornavigator) {
	function addEventListener<"load">(type: "load", listener: (this: Window, ev: Event) => any, options?: boolean | AddEventListenerOptions): void (+1 overload)addEventListener('load', function () {
		var navigator: Navigatornavigator.Navigator.serviceWorker: ServiceWorkerContainer

Available only in secure contexts.

MDN Reference

serviceWorker
.ServiceWorkerContainer.register(scriptURL: string | URL, options?: RegistrationOptions): Promise<ServiceWorkerRegistration>register('./path/to/service-worker.js');
}); }

服务工作者内部(Inside the service worker)

¥Inside the service worker

在服务工作线程中,你可以访问 $service-worker module,它为你提供所有静态资源、构建文件和预渲染页面的路径。你还将获得一个应用版本字符串,你可以使用它来创建唯一的缓存名称和部署的 base 路径。如果你的 Vite 配置指定 define(用于全局变量替换),这将应用于服务工作者以及你的服务器/客户端构建。

¥Inside the service worker you have access to the $service-worker module, which provides you with the paths to all static assets, build files and prerendered pages. You’re also provided with an app version string, which you can use for creating a unique cache name, and the deployment’s base path. If your Vite config specifies define (used for global variable replacements), this will be applied to service workers as well as your server/client builds.

以下示例预缓存构建的应用和 static 中的任何文件,并在发生所有其他请求时缓存它们。这将使每个页面在访问后都可以离线工作。

¥The following example caches the built app and any files in static eagerly, and caches all other requests as they happen. This would make each page work offline once visited.

/// <reference types="@sveltejs/kit" />
import { const build: string[]

An array of URL strings representing the files generated by Vite, suitable for caching with cache.addAll(build). During development, this is an empty array.

build
, const files: string[]

An array of URL strings representing the files in your static directory, or whatever directory is specified by config.kit.files.assets. You can customize which files are included from static directory using config.kit.serviceWorker.files

files
, const version: string

See config.kit.version. It’s useful for generating unique cache names inside your service worker, so that a later deployment of your app can invalidate old caches.

version
} from '$service-worker';
// Create a unique cache name for this deployment const const CACHE: stringCACHE = `cache-${const version: string

See config.kit.version. It’s useful for generating unique cache names inside your service worker, so that a later deployment of your app can invalidate old caches.

version
}`;
const const ASSETS: string[]ASSETS = [ ...const build: string[]

An array of URL strings representing the files generated by Vite, suitable for caching with cache.addAll(build). During development, this is an empty array.

build
, // the app itself
...const files: string[]

An array of URL strings representing the files in your static directory, or whatever directory is specified by config.kit.files.assets. You can customize which files are included from static directory using config.kit.serviceWorker.files

files
// everything in `static`
]; var self: Window & typeof globalThisself.function addEventListener(type: string, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void (+1 overload)

Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.

The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options’s capture.

When set to true, options’s capture prevents callback from being invoked when the event’s eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event’s eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event’s eventPhase attribute value is AT_TARGET.

When set to true, options’s passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.

When set to true, options’s once indicates that the callback will only be invoked once after which the event listener will be removed.

If an AbortSignal is passed for options’s signal, then the event listener will be removed when signal is aborted.

The event listener is appended to target’s event listener list and is not appended if it has the same type, callback, and capture.

MDN Reference

addEventListener
('install', (event: Eventevent) => {
// Create a new cache and add all files to it async function function (local function) addFilesToCache(): Promise<void>addFilesToCache() { const const cache: Cachecache = await var caches: CacheStorage

Available only in secure contexts.

MDN Reference

caches
.CacheStorage.open(cacheName: string): Promise<Cache>open(const CACHE: stringCACHE);
await const cache: Cachecache.Cache.addAll(requests: Iterable<RequestInfo>): Promise<void> (+1 overload)addAll(const ASSETS: string[]ASSETS); } event: Eventevent.waitUntil(function (local function) addFilesToCache(): Promise<void>addFilesToCache()); }); var self: Window & typeof globalThisself.function addEventListener(type: string, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void (+1 overload)

Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.

The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options’s capture.

When set to true, options’s capture prevents callback from being invoked when the event’s eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event’s eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event’s eventPhase attribute value is AT_TARGET.

When set to true, options’s passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.

When set to true, options’s once indicates that the callback will only be invoked once after which the event listener will be removed.

If an AbortSignal is passed for options’s signal, then the event listener will be removed when signal is aborted.

The event listener is appended to target’s event listener list and is not appended if it has the same type, callback, and capture.

MDN Reference

addEventListener
('activate', (event: Eventevent) => {
// Remove previous cached data from disk async function function (local function) deleteOldCaches(): Promise<void>deleteOldCaches() { for (const const key: stringkey of await var caches: CacheStorage

Available only in secure contexts.

MDN Reference

caches
.CacheStorage.keys(): Promise<string[]>keys()) {
if (const key: stringkey !== const CACHE: stringCACHE) await var caches: CacheStorage

Available only in secure contexts.

MDN Reference

caches
.CacheStorage.delete(cacheName: string): Promise<boolean>delete(const key: stringkey);
} } event: Eventevent.waitUntil(function (local function) deleteOldCaches(): Promise<void>deleteOldCaches()); }); var self: Window & typeof globalThisself.function addEventListener(type: string, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void (+1 overload)

Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.

The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options’s capture.

When set to true, options’s capture prevents callback from being invoked when the event’s eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event’s eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event’s eventPhase attribute value is AT_TARGET.

When set to true, options’s passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.

When set to true, options’s once indicates that the callback will only be invoked once after which the event listener will be removed.

If an AbortSignal is passed for options’s signal, then the event listener will be removed when signal is aborted.

The event listener is appended to target’s event listener list and is not appended if it has the same type, callback, and capture.

MDN Reference

addEventListener
('fetch', (event: Eventevent) => {
// ignore POST requests etc if (event: Eventevent.request.method !== 'GET') return; async function function (local function) respond(): Promise<Response>respond() { const const url: URLurl = new var URL: new (url: string | URL, base?: string | URL) => URL

The URL interface represents an object providing static methods used for creating object URLs.

MDN Reference

URL class is a global reference for require('url').URL https://nodejs.org/api/url.html#the-whatwg-url-api

@sincev10.0.0
URL
(event: Eventevent.request.url);
const const cache: Cachecache = await var caches: CacheStorage

Available only in secure contexts.

MDN Reference

caches
.CacheStorage.open(cacheName: string): Promise<Cache>open(const CACHE: stringCACHE);
// `build`/`files` can always be served from the cache if (const ASSETS: string[]ASSETS.Array<string>.includes(searchElement: string, fromIndex?: number): boolean

Determines whether an array includes a certain element, returning true or false as appropriate.

@paramsearchElement The element to search for.
@paramfromIndex The position in this array at which to begin searching for searchElement.
includes
(const url: URLurl.URL.pathname: stringpathname)) {
const const response: Response | undefinedresponse = await const cache: Cachecache.Cache.match(request: RequestInfo | URL, options?: CacheQueryOptions): Promise<Response | undefined>match(const url: URLurl.URL.pathname: stringpathname); if (const response: Response | undefinedresponse) { return const response: Responseresponse; } } // for everything else, try the network first, but // fall back to the cache if we're offline try { const const response: Responseresponse = await function fetch(input: string | URL | globalThis.Request, init?: RequestInit): Promise<Response> (+1 overload)fetch(event: Eventevent.request); // if we're offline, fetch can return a value that is not a Response // instead of throwing - and we can't pass this non-Response to respondWith if (!(const response: Responseresponse instanceof
var Response: {
    new (body?: BodyInit | null, init?: ResponseInit): Response;
    prototype: Response;
    error(): Response;
    json(data: any, init?: ResponseInit): Response;
    redirect(url: string | URL, status?: number): Response;
}

This Fetch API interface represents the response to a request.

MDN Reference

Response
)) {
throw new
var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error
('invalid response from fetch');
} if (const response: Responseresponse.Response.status: numberstatus === 200) { const cache: Cachecache.Cache.put(request: RequestInfo | URL, response: Response): Promise<void>put(event: Eventevent.request, const response: Responseresponse.Response.clone(): Responseclone()); } return const response: Responseresponse; } catch (function (local var) err: unknownerr) { const const response: Response | undefinedresponse = await const cache: Cachecache.Cache.match(request: RequestInfo | URL, options?: CacheQueryOptions): Promise<Response | undefined>match(event: Eventevent.request); if (const response: Response | undefinedresponse) { return const response: Responseresponse; } // if there's no cache, then just error out // as there is nothing we can do to respond to this request throw function (local var) err: unknownerr; } } event: Eventevent.respondWith(function (local function) respond(): Promise<Response>respond()); });

缓存时要小心!在某些情况下,过时的数据可能比离线时不可用的数据更糟糕。由于浏览器会在缓存太满时清空缓存,因此你还应该小心缓存视频文件等大型资源。

¥[!NOTE] Be careful when caching! In some cases, stale data might be worse than data that’s unavailable while offline. Since browsers will empty caches if they get too full, you should also be careful about caching large assets like video files.

开发期间(During development)

¥During development

服务工作者打包用于生产,但不用于开发。因此,只有支持 服务工作者中的模块 的浏览器才能在开发时使用它们。如果你手动注册服务工作者,则需要在开发中传递 { type: 'module' } 选项:

¥The service worker is bundled for production, but not during development. For that reason, only browsers that support modules in service workers will be able to use them at dev time. If you are manually registering your service worker, you will need to pass the { type: 'module' } option in development:

import { const dev: boolean

Whether the dev server is running. This is not guaranteed to correspond to NODE_ENV or MODE.

dev
} from '$app/environment';
var navigator: Navigatornavigator.Navigator.serviceWorker: ServiceWorkerContainer

Available only in secure contexts.

MDN Reference

serviceWorker
.ServiceWorkerContainer.register(scriptURL: string | URL, options?: RegistrationOptions): Promise<ServiceWorkerRegistration>register('/service-worker.js', {
RegistrationOptions.type?: WorkerType | undefinedtype: const dev: boolean

Whether the dev server is running. This is not guaranteed to correspond to NODE_ENV or MODE.

dev
? 'module' : 'classic'
});

buildprerendered 在开发期间是空数组

¥[!NOTE] build and prerendered are empty arrays during development

类型安全(Type safety)

¥Type safety

为服务工作者设置适当的类型需要一些手动设置。在你的 service-worker.js 中,将以下内容添加到文件顶部:

¥Setting up proper types for service workers requires some manual setup. Inside your service-worker.js, add the following to the top of your file:

/// <reference types="@sveltejs/kit" />
/// <reference no-default-lib="true"/>
/// <reference lib="esnext" />
/// <reference lib="webworker" />

const sw = /** @type {ServiceWorkerGlobalScope} */ (/** @type {unknown} */ (self));
/// <reference types="@sveltejs/kit" />
/// <reference no-default-lib="true"/>
/// <reference lib="esnext" />
/// <reference lib="webworker" />

const sw = self as unknown as ServiceWorkerGlobalScope;

这会禁用对 DOM 类型(如 HTMLElement)的访问,这些类型在服务工作线程中不可用,并实例化正确的全局变量。将 self 重新分配给 sw 允许你在过程中对其进行类型转换(有几种方法可以做到这一点,但这是最简单的方法,不需要额外的文件)。在文件的其余部分使用 sw 而不是 self。对 SvelteKit 类型的引用确保 $service-worker 导入具有正确的类型定义。如果你导入 $env/static/public,则必须对导入进行 // @ts-ignore 操作或将 /// <reference types="../.svelte-kit/ambient.d.ts" /> 添加到引用类型中。

¥This disables access to DOM typings like HTMLElement which are not available inside a service worker and instantiates the correct globals. The reassignment of self to sw allows you to type cast it in the process (there are a couple of ways to do this, but this is the easiest that requires no additional files). Use sw instead of self in the rest of the file. The reference to the SvelteKit types ensures that the $service-worker import has proper type definitions. If you import $env/static/public you either have to // @ts-ignore the import or add /// <reference types="../.svelte-kit/ambient.d.ts" /> to the reference types.

其他解决方案(Other solutions)

¥Other solutions

SvelteKit 的服务工作线程实现旨在易于使用,对于大多数用户来说可能是一个很好的解决方案。但是,在 SvelteKit 之外,许多 PWA 应用都利用了 Workbox 库。如果你习惯使用 Workbox,你可能更喜欢 Vite PWA 插件

¥SvelteKit’s service worker implementation is designed to be easy to work with and is probably a good solution for most users. However, outside of SvelteKit, many PWA applications leverage the Workbox library. If you’re used to using Workbox you may prefer Vite PWA plugin.

参考(References)

¥References

有关服务工作者的更多一般信息,我们推荐 MDN 网络文档

¥For more general information on service workers, we recommend the MDN web docs.