jeena/en.javascript.info
1
0
Fork 0
Code Issues Pull requests Projects Packages Wiki Activity Actions

minor fixes

Browse source
This commit is contained in:
Ilya Kantor 2019-07-04 22:21:34 +03:00
parent b1b66a3065
commit 8365ea7163
6 changed files with 22 additions and 22 deletions
Download patch file Download diff file Expand all files Collapse all files

12
1-js/11-async/07-microtask-queue/article.md
View file

@ -21,7 +21,7 @@ That's strange, because the promise is definitely done from the beginning.
Why did the `.then` trigger afterwards? What's going on?
## Microtasks
## Microtasks queue
Asynchronous tasks need proper management. For that, the standard specifies an internal queue `PromiseJobs`, more often referred to as "microtask queue" (v8 term).
@ -68,7 +68,7 @@ let promise = Promise.reject(new Error("Promise Failed!"));
promise.catch(err => alert('caught'));
*/!*
// no error, all quiet
// doesn't run: error handled
window.addEventListener('unhandledrejection', event => alert(event.reason));
```
@ -93,13 +93,13 @@ setTimeout(() => promise.catch(err => alert('caught')), 1000);
window.addEventListener('unhandledrejection', event => alert(event.reason));
```
Now, if you run it, we'll see `Promise Failed!` message first, and then `caught`.
Now, if you run it, we'll see `Promise Failed!` message first, and then `caught`.
If we didn't know about microtasks, we could wonder: "Why did `unhandledrejection` happen? We did catch the error!".
If we didn't know about microtasks queue, we could wonder: "Why did `unhandledrejection` handler run? We did catch the error!".
But now we do know that `unhandledrejection` is generated when the microtask queue is complete: the engine examines promises and, if any of them is in "rejected" state, then the event triggers.
But now we understand that `unhandledrejection` is generated when the microtask queue is complete: the engine examines promises and, if any of them is in "rejected" state, then the event triggers.
...By the way, the `.catch` added by `setTimeout` also triggers, of course it does, but later, after `unhandledrejection` has already occurred.
In the example above, `.catch` added by `setTimeout` also triggers, but later, after `unhandledrejection` has already occurred, so that doesn't change anything.
## Summary