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

This is a _lot_ to wade through, so apologies if this has already been answered... But what happens in this scenario?

1. you get a cancelable promise `data`
2. it resolves as expected.
3. then you keep it around because you want the cached value.
4. you call cancel on it: `data.cancel()`
5. you "subscribe" to it again with a `then` call.

If it's cancelled after it's resolved, and then you `then` it out again, do you still get the value?

What happens if you cancel while processing the resolution? Will the following still log a value? I mean, I'd *think* it would, but I really don't know.

```js
cancelablePromise.then(x => {
  cancelablePromise.cancel();
  return x;
}).then(x => console.log('here', x));
```

For all of the times I've derided Promises for not being cancelable, it's the lack of cancellation that is one of Promise's strongest traits. The name even says it, it's a "Promise", it's a guarantee. Adding cancellation would pollute the type and have implications for any "thennable". I think @jhusain was onto something with the idea that it should be a different type. Not necessarily Promise-shaped, and probably not an Observable either. Something more like a single value Observable-type-thing.

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/27#issuecomment-176024409