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Promise API #73

dherman opened this issue Apr 21, 2016 · 2 comments


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@dherman dherman commented Apr 21, 2016

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).


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@winding-lines winding-lines commented Jul 22, 2016

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


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@pitaj pitaj commented Jul 15, 2018

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

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
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