Queuing promises

Question

I use mbostock/queue for queuing few async operation. It is more to rate limit (UI generate few events, where the backend can process it slowly), and also to make sure they

Answer 1

The short answer is no, you don't need an extra library. Promise.then() is sufficiently "atomic". The long answer is: it's worth making a queue() function to keep code DRY. Bluebird-promises seems pretty complete, but here's something based on AngularJS's $q.

If I was making .queue() I'd want it to handle errors as well.

Here's an angular service factory, and some use cases:

/**
 * Simple promise factory
 */

angular.module('app').factory('P', function($q) {
  var P = $q;

  // Make a promise
  P.then = function(obj) {
    return $q.when(obj);
  };

  // Take a promise.  Queue 'action'.  On 'action' faulure, run 'error' and continue.
  P.queue = function(promise, action, error) {
    return promise.then(action).catch(error);
  };

  // Oook!  Monkey patch .queue() onto a $q promise.
  P.startQueue = function(obj) {
    var promise = $q.when(obj);
    promise.queue = function(action, error) {
      return promise.then(action).catch(error);
    };
    return promise;
  };

  return P;
});

How to use it:

.run(function($state, YouReallyNeedJustQorP, $q, P) {

  // Use a $q promise.  Queue actions with P

  // Make a regular old promise
  var myPromise = $q.when('plain old promise');

  // use P to queue an action on myPromise
  P.queue(myPromise, function() { return console.log('myPromise: do something clever'); });

  // use P to queue an action
  P.queue(myPromise, function() {
    throw console.log('myPromise: do something dangerous');
  }, function() { 
    return console.log('myPromise: risks must be taken!');
  });
  // use P to queue an action
  P.queue(myPromise, function() { return console.log('myPromise: never quit'); });


  // Same thing, but make a special promise with P

  var myQueue = P.startQueue(myPromise);

  // use P to queue an action
  myQueue.queue(function() { return console.log('myQueue: do something clever'); });

  // use P to queue an action
  myQueue.queue(function() {
    throw console.log('myQueue: do something hard');
  }, function() { 
    return console.log('myQueue: hard is interesting!');
  });
  // use P to queue an action
  myQueue.queue(function() { return console.log('myQueue: no easy days'); });