Fix 11494: promise handling in WritableStreamDefaultWriter example

[wbamberg]

Fixes #11494, I hope.

This PR rewrites the example to use await.

In the issue report I was a bit puzzled by this bit:

defaultWriter.ready.then is called multiple times.

As far as I can see you have to call ready after each time you write to the stream, so you know you can write to it again. However it is true that:

• if any chunk write throws an error, then the writer keeps writing (and keeps getting errors), when it should presumably give up
• defaultWriter.close(); should presumably return its promise, or any error is unhandled

One change I have made here is no longer distinguishing between a chunk write failing and defaultWriter.close(); failing: they're all in the same try block. That is simpler and seemed OK?

Anyway if you like this I'll update all the other places it's used, as well as the working copy in mdn/dom-examples.

I've tested this and it seems to work fine. I've also tested it with write throwing an error: in the old version the output was like:

---

---

...and in this version it is like:

---

[github-actions]

Preview URLs

• /en-US/docs/Web/API/WritableStreamDefaultWriter

(comment last updated: 2023-03-24 05:35:49)

[teoli2003]

This is much better, and demonstrates how await improve code readability, too. I'm not merging it in case others want to review it, but feel free to merge it!