Experimental: 这是一个实验中的功能


使用 ServiceWorkerGlobalScope.onfetch (en-US)或addEventListener监听.
该事件回调会注入FetchEvent参数.它携带了有关请求和结果响应的信息以及方法FetchEvent.respondWith() ,允许我们向受控页面提供任意响应.


FetchEvent.FetchEvent() (en-US)
Creates a new FetchEvent object.


Inherits properties from its ancestor, Event.

FetchEvent.isReload (en-US) 只读
Returns a Boolean that is true if the event was dispatched with the user's intention for the page to reload, and false otherwise. Typically, pressing the refresh button in a browser is a reload, while clicking a link and pressing the back button is not.
FetchEvent.request (en-US) 只读
Returns the Request that triggered the event handler.
FetchEvent.clientId (en-US) 只读
Returns the id of the client that the current service worker is controlling.

Deprecated properties

FetchEvent.client (en-US) 只读
Returns the Client that the current service worker is controlling.


Inherits methods from its parent, ExtendableEvent.

Resolves by returning a Response or a network error  to Fetch.

Extends the lifetime of the event.  It is intended to be called in the install event handler for the installing (en-US) worker and on the active event handler for the active worker.


This code snippet is from the service worker fetch sample (run the fetch sample live). In an earlier part of the code,  an InstallEvent controls caching of a number of resources. The ServiceWorkerGlobalScope.onfetch (en-US) event handler then listens for the fetch event. When fired, FetchEvent.respondWith() returns a promise back to the controlled page. This promise resolves to the first matching URL request in the Cache object. If no match is found (i.e. that resource wasn't cached in the install phase), the code fetches a response from the network.

The code also handles exceptions thrown from the ServiceWorkerGlobalScope.fetch() (en-US) operation. Note that a HTTP error response (e.g., 404) doesn't trigger an exception. It returns a normal response object that has the appropriate error code set.

self.addEventListener('fetch', function(event) {
  console.log('Handling fetch event for', event.request.url);

    caches.match(event.request).then(function(response) {
      if (response) {
        console.log('Found response in cache:', response);

        return response;
      console.log('No response found in cache. About to fetch from network...');

      return fetch(event.request).then(function(response) {
        console.log('Response from network is:', response);

        return response;
      }).catch(function(error) {
        console.error('Fetching failed:', error);

        throw error;


Specification Status Comment
Service Workers
Working Draft Initial definition.


We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help! (en-US)
Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 40.0 44.0 (44.0)[1] 未实现 24 未实现
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support 未实现 ? 44.0 (44.0) (Yes) 未实现 ? 未实现 44.0

[1] Service workers (and Push) have been disabled in the Firefox 45 and 52 Extended Support Releases (ESR.)