Questions: will nodejs expose SetPromiseHook of V8 as javascript API in the future?

[JiaLiPassion]

• Version:
• Platform:
• Subsystem:

in the newest nodejs,

1. the async_wrap and async_hooks have been implemented in async_hooks initial implementation #11883.
2. addPromiseHook have been exposed in domain: support promises #12489

I want to ask that will addPromiseHook be exposed as Javascript API? Or it will also use the async_wrap to intercept the promise lifecycle?

The reason I asked is I want to implement an async_hooks version zone.js to resolve the
native async/await issue. currently native async/await of nodejs use native v8 promise and can't be tracked by javascript module.

Thank you!

[addaleax]

I want to ask that will addPromiseHook be exposed as Javascript API?

I don’t think that’s likely, but you can open a PR and see where that goes if you really want.

Or it will also use the async_wrap to intercept the promise lifecycle?

I’m not sure, but maybe #13000 (Promise support for async_hooks) is the answer to your question?

[JiaLiPassion]

@addaleax , thank you very much for your reply, I will look into #13000.

[AndreasMadsen]

@JiaLiPassion Why is async_hooks not sufficient? If you want to implement Zones you will need more than just promise hooks. I can see that zone.js uses async-listener, async_hooks is a core-supported alternative to that and it will support promises.

If you just want the promise part you can filter all events in async_hooks by the provider parameter, the extra overhead should be very small. If async_hooks is not enough and you need more information, then I think that is the best place to start a discussion.

[JiaLiPassion]

@AndreasMadsen , thanks for reply, in fact zone.js not use async-listener, it just monkey-patch all native async APIs, such as promise, setTimeout and so on.

Now zone.js monkey-patch those APIs in nodejs.

1. setTimeout/Immediate/Interval
2. Promise
3. EventEmitter
4. process.nextTick
5. fs
6. crypto

https://github.com/angular/zone.js/blob/master/STANDARD-APIS.md

So if async_hooks will support all async APIs, I think it will be ok for re-implement zone.js with the new async_hooks.

I just began to read the document about async_hooks, and I will try to find out how to use it.

If you just want the promise part you can filter all events in async_hooks by the provider parameter, the extra overhead should be very small. If async_hooks is not enough and you need more information, then I think that is the best place to start a discussion.

Thank you for the information, basically I want to use all events with async_hooks, but I may want the provider for some logic, is there any document for this parameter? I didn't find it in here, https://github.com/nodejs/node-eps/blob/master/006-asynchooks-api.md

edit by @AndreasMadsen: fixed quote formatting.

[AndreasMadsen]

So if async_hooks will support all async APIs, I think it will be ok for re-implement zone.js with the new async_hooks.

if it doesn't it is a bug :)

Thank you for the information, basically I want to use all events with async_hooks, but I may want the provider for some logic, is there any document for this parameter? I didn't find it in here, https://github.com/nodejs/node-eps/blob/master/006-asynchooks-api.md

Sorry, it is now called type it is a parameter in the init hook.

PS: I recommend looking at dprof as a starting example, as it uses most of the async_hooks feature. Note that it currently uses and older API, there is a PR for the new API.

[JiaLiPassion]

@AndreasMadsen , thank you very much, I will try to re-implement zone.js with async_hooks.

And the promise support with async_hooks will be implemented until #13000 is merged, is that right?

[AndreasMadsen]

And the promise support with async_hooks will be implemented until #13000 is merged, is that right?

Yes, you will have to wait on #13000 to get merged before promises are supported by async_hooks. I maintain the async_hooks tracking issue that you can follow: nodejs/diagnostics#29

[JiaLiPassion]

@AndreasMadsen , thank you, I will keep track with nodejs/diagnostics#29 and #13000.

[addaleax]

Cool, I’ll close this as an answered question then. If you have any further questions, feel free to ask here!