The preloadResponse
read-only property of the FetchEvent
interface returns a Promise
that resolves to the navigation preload Response
if navigation preload was triggered or undefined otherwise.
Syntax
var expectedResponse = fetchEvent.preloadResponse;
Value
A Promise
that resolves to a Response
or otherwise to undefined
.
Example
This code snippet is from the navigation preload page. The ServiceWorkerGlobalScope.onfetch
event handler listens for the fetch
event. When fired, pass a promise that back to the controlled page to FetchEvent.respondWith()
. 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 'preloadResponse' in that specification. |
Working Draft | Initial definition. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
preloadResponse | Chrome Full support 59 | Edge Full support 18 | Firefox ? | IE No support No | Opera Full support 46 | Safari No support No | WebView Android Full support 59 | Chrome Android Full support 59 | Firefox Android ? | Opera Android Full support 43 | Safari iOS No support No | Samsung 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.