ExtendableEvent

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  1. Constructor
  2. Properties
  3. Methods
  4. Examples
  5. Specifications
  6. Browser compatibility
  7. See also

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这是一个实验中的功能
此功能某些浏览器尚在开发中，请参考浏览器兼容性表格以得到在不同浏览器中适合使用的前缀。由于该功能对应的标准文档可能被重新修订，所以在未来版本的浏览器中该功能的语法和行为可能随之改变。

The ExtendableEvent interface extends the lifetime of the install and activate events dispatched on the global scope as part of the service worker lifecycle. This ensures that any functional events (like FetchEvent) are not dispatched until it upgrades database schemas and deletes the outdated cache entries.

If waitUntil() is called outside of the ExtendableEvent handler, the browser should throw an InvalidStateError; note also that multiple calls will stack up, and the resulting promises will be added to the list of extend lifetime promises.

Note: The behaviour described in the above paragraph was fixed in Firefox 43 (see bug 1189644.)

This interface inherits from the Event interface.

Note: This interface is only available when the global scope is a ServiceWorkerGlobalScope. It is not available when it is a Window, or the scope of another kind of worker.

Constructor

ExtendableEvent()
Creates a new ExtendableEvent object.

Properties

Doesn't implement any specific properties, but inherits properties from its parent, Event.

Methods

Inherits methods from its parent, Event.

ExtendableEvent.waitUntil()

Extends the lifetime of the event.  It is intended to be called in the install EventHandler for the installing worker and on the active EventHandler for the active worker.

Examples

This code snippet is from the service worker prefetch sample (see prefetch example live.) The code calls ExtendableEvent.waitUntil() in ServiceWorkerGlobalScope.oninstall, delaying treating the ServiceWorkerRegistration.installing worker as installed until the passed promise resolves successfully. The promise resolves when all resources have been fetched and cached, or else when any exception occurs.

The code snippet also shows a best practice for versioning caches used by the service worker. Though there's only one cache in this example, the same approach can be used for multiple caches. It maps a shorthand identifier for a cache to a specific, versioned cache name.

Note: In Chrome, logging statements are visible via the "Inspect" interface for the relevant service worker accessed via chrome://serviceworker-internals.

var CACHE_VERSION = 1;
var CURRENT_CACHES = {
  prefetch: 'prefetch-cache-v' + CACHE_VERSION
};

self.addEventListener('install', function(event) {
  var urlsToPrefetch = [
    './static/pre_fetched.txt',
    './static/pre_fetched.html',
    'https://www.chromium.org/_/rsrc/1302286216006/config/customLogo.gif'
  ];

  console.log('Handling install event. Resources to pre-fetch:', urlsToPrefetch);

  event.waitUntil(
    caches.open(CURRENT_CACHES['prefetch']).then(function(cache) {
      cache.addAll(urlsToPrefetch.map(function(urlToPrefetch) {
        return new Request(urlToPrefetch, {mode: 'no-cors'});
      })).then(function() {
        console.log('All resources have been fetched and cached.');
      });
    }).catch(function(error) {
      console.error('Pre-fetching failed:', error);
    })
  );
});
Important: When fetching resources, it's very important to use {mode: 'no-cors'} if there is any chance that the resources are served off of a server that doesn't support CORS. In this example, www.chromium.org doesn't support CORS.

Specifications

Specification Status Comment
Service Workers
ExtendableEvent		 Working Draft Initial definition.

Browser compatibility

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!
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
async waitUntil() ? 53.0 (53.0)[2] 未实现 ? 未实现
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support 未实现 44.0 (44.0) 未实现 ? 未实现 40.0
async waitUntil() 未实现 53.0 (53.0)[2] 未实现 ? 未实现 ?

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

[2] ExtendableEvent.waitUntil() can now be called asynchronously (see bug 1263304).

See also

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