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This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The respondWith() method of the FetchEvent interface is intended for containing code that generates custom responses to the requests coming from the controlled page. This code will resolve by returning a Response or network error to Fetch.

Renderer-side security checks about tainting for cross-origin content are tied to the transparency (or opacity) of the Response body, not URLs. If the request is a top-level navigation and the return value is a Response whose type attribute is opaque (i.e. an opaque response body), a network error is returned to Fetch. The final URL of all successful (non network-error) responses is the requested URL.


  //Promise that resolves to a Response or a network error.




Any custom response-generating code.


This code snippet is from the service worker fetch sample (run the fetch sample live.) 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 fetches a response from the network.

The code also handles exceptions thrown from the ServiceWorkerGlobalScope.fetch operation. Note that an HTTP error response (e.g., 404) will not trigger an exception. It will return 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
The definition of 'respondWith()' in that specification.
Working Draft Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 40.0 44.0 (44.0)[1] No support 24 No support
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support ? 44.0 (44.0) (Yes) No support ? No support 44.0

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

See also

Document Tags and Contributors

 Contributors to this page: chrisdavidmills, spleen387, Sebastianz, fscholz, kscarfone, teoli, jpmedley
 Last updated by: chrisdavidmills,