Promise.all in JavaScript: How to get resolve value for all promises?

First question

Promise.all takes an array of promises

Change:

Promise.all(read_csv_file("devices.csv"), read_csv_file("bugs.csv"))

to (add [] around arguments)

Promise.all([read_csv_file("devices.csv"), read_csv_file("bugs.csv")])
// ---------^-------------------------------------------------------^

Second question

The Promise.all resolves with an array of results for each of the promises you passed into it.

This means you can extract the results into variables like:

Promise.all([read_csv_file("devices.csv"), read_csv_file("bugs.csv")])
  .then(function(results) {
    var first = results[0];  // contents of the first csv file
    var second = results[1]; // contents of the second csv file
  });

You can use ES6+ destructuring to further simplify the code:

Promise.all([read_csv_file("devices.csv"), read_csv_file("bugs.csv")])
  .then(function([first, second]) {

  });

Answer to your second question:

If you want the then callback to accept two different arguemnts, then you can use Bluebird and its spread method. See:

• http://bluebirdjs.com/docs/api/spread.html

Instead of .then(function (array) { ... }) and having to access array[0] and array[1] inside of your then handler you will be able to use spread(function (value1, value2) { ... }) and have both variables named as you want.

This is a feature of Bluebird, it's not possible with plain Promise.

You use Bluebird just like Promise, e.g.:

var P = require('bluebird');
// and in your code:
return new P(function (resolve, reject) { ...
// instead of:
return new Promise(function (resolve, reject) { ...

Of course you don't have to name it P but whatever you want.

For more examples see the Bluebird Cheatsheets.