The request
read-only property of the FetchEvent
interface returns the Request
that triggered the event handler.
This property is non-nullable (since version 46, in the case of Firefox.) If a request is not provided by some other means, the constructor options
object must contain a request (see FetchEvent()
.)
This code snippet is from the service worker fetch sample (run the fetch sample live). The 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 fetches a response from the network.
The code also handles exceptions thrown from the 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", (event) => {
console.log("Handling fetch event for", event.request.url);
event.respondWith(
caches.match(event.request).then((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((response) => {
console.log("Response from network is:", response);
return response;
})
.catch((error) => {
console.error("Fetching failed:", error);
throw error;
});
}),
);
});