Re: [fetch] Aborting a fetch (#27)

Say you have a ServiceWorker with:

```js
self.addEventListener('fetch', function(event) {
  event.respondWith(
    fetch('/whatever.json').then(function(response) {
      return response.json();
    }).then(function(data) {
      return fetch(data.url);
    })
  );
});
```

Say this request is in progress and the user hits X in the browser UI, closes the tab, or navigates. The browser can cancel the stream once the promise it gets resolves, but it cannot abort either fetch or the `.json` read of the first fetch.

A chaining cancellable promise solves this problem, as the browser calls cancel, and the currently in-progress part of the promise chain is terminated.

Counter to some of the complaints in this thread, this is a case where you *do* want the receiver of the promise to have cancellation rights.

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/27#issuecomment-87754126