What is the best way to resolve Node.js promise?

Question

I try to call my native C++ function implemented with NAN(Native Abstraction for Node.js) with a Promise Asynchronous. Unfortunately the Promise is never resolved. My Code in Javascript.

function callbackDoAsyncStuffFirst() {
  return new Promise(function (resolve, reject) {
    module.doAsyncStuffFirst(function (error, a, v, b) {
      if (error) {
        return reject(error);
      }
      console.log("Resolve First: ", a, " ", b, " ", v, " ");
      let ret = [a, b, v];
      console.log("Return frist Resolve");
      return resolve(ret);
    });
  });
}

function callbackDoAsyncStuff() {
  return new Promise(function (resolve, reject) {
    module.doAsyncStuffSecond(function (error, a, b) {
      if (error) {
        return reject(error);
      }
      console.log("Returned: ", a, " ", b);
      let ret = [a, b];
      console.log("Call Second Resolve");
      return resolve(ret);
    }, 'valueA', 'valueB');
  });
}

let p = callbackDoAsyncStuffFirst().then((retArray) => { console.log("resolve first-->", retArray) });

let second = callbackDoAsyncStuff().then((retArray) => { console.log("resolve second-->: ", retArray) });

The console output looks like

C++: Start Execute
C++: HandleOKCallback
JS: Resolve First:  a, b, v
JS: Return frist Resolve

After this nothing happens any more.

Answer 1

This fake module demonstrates that the problem is in your C++ plugin, not in your JavaScript, which works correctly here.

It also demonstrates how to call the callback with a "successful" set of arguments, in that the first callback argument you are interpreting as an error, which must be falsey in order for you not to reject your promise.

 var module = { doAsyncStuffFirst: (cb) => { cb(undefined, 'dummy_a1', 'dummy_v1', 'dummy_b1'); }, doAsyncStuffSecond: (cb) => { cb(undefined, 'dummy_a2', 'dummy_b2'); } } function callbackDoAsyncStuffFirst() { return new Promise(function (resolve, reject) { module.doAsyncStuffFirst(function (error, a, v, b) { if (error) { return reject(error); } console.log("Resolve First: ", a, " ", b, " ", v, " "); let ret = [a, b, v]; console.log("Return frist Resolve"); return resolve(ret); }); }); } function callbackDoAsyncStuff() { return new Promise(function (resolve, reject) { module.doAsyncStuffSecond(function (error, a, b) { if (error) { return reject(error); } console.log("Returned: ", a, " ", b); let ret = [a, b]; console.log("Call Second Resolve"); return resolve(ret); }, 'valueA', 'valueB'); }); } let p = callbackDoAsyncStuffFirst().then((retArray) => { console.log("resolve first-->", retArray) }); let second = callbackDoAsyncStuff().then((retArray) => { console.log("resolve second-->: ", retArray) });