如何在promise链中返回promise.map（bluebird）？

Question

I'm using a chain to control flow and can't get promise.map in step2() to wait until all of it's generated promises are resolved.

Here's a visual of the flow I'm trying to achieve.

step1() step2() step2() step2() step2() step3()

In step2() I'm using Bluebird's promise.map.

Here's the chain:

step1()
  .then(function() { return step2() }) 
  .then(function() { return step3() })
  .catch(function() { // handle errors })

Here's my functions for each step:

let step1 = function() {
  return new Promise(function(resolve, reject) {      
    // do stuff
    resolve()
  })
}

let step2 = function() {
  return new Promise(function(resolve, reject) {
    things = []      
    return Promise.map(things, function(thing) {
      // load file async with callback
    })
    resolve()
  })
}

let step3 = function() {
  return new Promise(function(resolve, reject) {      
    // do stuff
    resolve()
  })
}

I've tested the chain with many more steps each with a timeout and it worked as expected with the exception of the promise.map in step2() . What am I doing wrong? :)

Answer 1

The problem is from step 2. Promise.map already return promise, so you can just return it to callee. Then you warp the async function with callback with new Promise .

let step2 = function() {
  things = []      
  return Promise.map(things, function(thing) {
    // load file async with callback
    return new Promise(function(resolve, reject) {
      fileAsyncFunc(thing, function callback(err, data) {
        if(err) {
          reject(err);
          return;
        }
        resolve(data);
      });
    });
  });
}

Answer 2

You are not calling your resolve callback properly.

let step2 = function() {
    things = []      
    return Promise.map(things, function(thing) {         
      return new Promise( function( resolve, reject ) {
          // load file async with callback
          resolve(...)
      } )
    })
}

In your case resolve() is always called, since you are executing async function for loading the file.