Managing promise dependencies

Question

I\'m using Node.js and Bluebird to create some fairly complicated logic involving uncompressing a structured file, parsing JSON, creating and making changes to several Mongo

Answer 1

It is certainly not an antipattern to return promises within thens, flattening nested promises is a feature of the promise spec.

Here's a possible rewrite, though I'm not sure it's cleaner:

var doStuff = function () {

  promise1()
  .then(function (value1) {

    return promise2()
    .then(function (value2) {

      return promise3(value1)
      .then(successFunction)
      .finally(function() {
        cleanup(null, value1, value2);
      });

    })
    .finally(function() {
      cleanup(null, value1, null);
    });

  })
  .finally(function () {
    cleanup(null, null, null);
  });

};

Or another option, with atomic cleanup functions:

var doStuff = function () {

  promise1()
  .then(function (value1) {

    return promise2()
    .then(function (value2) {

      return promise3(value1)
      .then(successFunction)
      .finally(function() {
        cleanup3(value2);
      });

    })
    .finally(function() {
      cleanup2(value1);
    });

  })
  .finally(function (err) {
    cleanup1(err);
  });

};

Really, I feel like there's not much you can do to clean this up. Event with vanilla try/catches, the best possible pattern is pretty similar to these.