Fetch
The Fetch API provides an interface for asynchronously fetching resources via HTTP requests inside of a Worker.
The fetch method is implemented on the ServiceWorkerGlobalScope. Refer to MDN documentation for more information.
 Constructor
addEventListener('fetch', event => {  // NOTE: can’t use fetch here, as we’re not in an async scope yet  event.respondWith(eventHandler(event));
});
async function eventHandler(event) {  // fetch can be awaited here since `event.respondWith()` waits for the Promise it receives to settle  const resp = await fetch(event.request);  return resp;
}
fetch()Promise{<Response>}- Fetch returns a promise to a Response.
 
 Properties
requestRequest|string- The 
Requestobject or a string represents the URL to fetch. 
- The 
 initRequestInit- The content of the request.