FetchEvent.PreloadResponse

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The preloadResponse read-only property of the FetchEvent interface returns the Request that triggered the event handler.

Syntax

var expectedResponse = FetchEvent.preloadResponse;

Value

A PreloadResponse promise.

Example

This code snippet is from the navigation preload page. The ServiceWorkerGlobalScope.onfetch event handler listens for the fetch event. When fired, FetchEvent.respondWith(any value) 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, the code checks for a preloaded response. Else it fetches a response from the network.

addEventListener('fetch', event => {
  event.respondWith(async function() {
    // Respond from the cache if we can
    const cachedResponse = await caches.match(event.request);
    if (cachedResponse) return cachedResponse;

    // Else, use the preloaded response, if it's there
    const response = await event.preloadResponse;
    if (response) return response;

    // Else try the network.
    return fetch(event.request);
  }());
});

Specifications

Specification Status Comment
Service Workers
The definition of 'FetchEvent' in that specification.
Working Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
preloadResponse
Experimental
Chrome Full support 59Edge Full support 18Firefox ? IE No support NoOpera Full support 46Safari No support NoWebView Android Full support 59Chrome Android Full support 59Edge Mobile ? Firefox Android ? Opera Android Full support 43Safari iOS No support NoSamsung Internet Android Full support 7.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.

See also

Document Tags and Contributors

Contributors to this page: estelle, keerthanak17
Last updated by: estelle,