Neon: Promise API

[dherman]

Expose the Promise object type under neon::js::promise::JsPromise, using v8::Promise. This one is going to require some good experimentation and thinking around the neon async story (see #26).

[winding-lines]

@dherman I finally have some time to play with neon, will check this out :)

[pitaj]

Just a few resources people might find handy if they want to try implementing this:

• The N-API has first-class Promise creation
• There's already an N-API sys crate, the higher-order crate is a WIP
• Here's an example of using the Promise creation is C++

Some other things to consider:

• Rust will soon? have first-class Future support, it would be good to provide an API to convert a Rust Future to a JS Promise
• As said in the example

Node.js will process the fulfillment/conclusion of the Promise in an asynchronous fashion (compared to "real-time" in JavaScript) because the fulfillment is added to the event loop's "Promise fulfillment microtask queue", which is processed immediately after the "nextTick microtask queue", even when it is fulfilled synchronously in C++.

If this ever becomes UNTRUE, then you would need to utilize an AsyncWorker (or a similar concept) in order to ensure this Promise is fulfilled asynchronously.

• Since the N-API is available since Node 8, it is worth considering supporting it for all Node versions >=8, with instead instructing developers to use a callback native API with a Promise on the JS side for versions older than that. Node 6 has less than a year of maintenance support left, after all.
• If that is not acceptable, then perhaps it is possible to automate doing that instead, or to provide a Promise through older C++ APIs. I'm unaware of nan supporting Promise creation though, so it would require more direct V8 APIs

[cdbattags]

Any update here with rust 1.39, future 0.3 and tokio 0.2 release?

Would love to do some experimentation wiring express.js controllers and actix-web services

[bochaco]

I was also wondering the same, I am looking for a way to bind async functions to JS Promises