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

@getify 

> Do both `"child1"` and `"child2"` still get printed? Or neither?

Well, you get `cancel is not a function` as those are regular promises, but I'll assume you were meant to create a cancellable promise :smile:. In your example, assuming `parent.cancel()` is called prior to it resolving, neither `"child1"` and `"child2"` is logged. This makes total sense to me, let me reword your example:

```js
var parent = new CancellablePromise(resolve => setTimeout(_ => resolve("Hello"), 100));
var child1 = parent.then(value => console.log(value + " world"));
var child2 = parent.then(value => console.log(value + " everyone"));
```

Is parent is cancelled before resolving, and you expected something to be logged, what would the value be?

> If … passing parent around to … different parts of a system … means that … one observer … can … decide … another part of the system … is prevented from knowing … what happens with parent

This isn't the case in my proposal, you can add a cancel observer in the same way you observe fulfill & reject. This would allow you to stop a spinner, but not display an error message, as cancellation often isn't error worthy.

> Now, what happens if instead `child1.cancel()`. Does that mean … "child2" … gets printed?

"child2" does get printed. The parent has a cancellable promise child count of 1 (`child2`) so it does not cancel.

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