Promises vs Callbacks

1-callbacks.js

// --------------------------------------------------------------------
// Standard callback-style

getUserID(function(err, id) {
  User.find(id, function(err, user) {
    Twitter.get('/statuses/user_timeline.json', user.username, function(err, data) {
      console.log(data);
    });
  });
});

// --------------------------------------------------------------------
// What if you need to handle errors?
// Things get messy:

getUserID(function(err, id) {
  if (err) { return error(err); }

  User.find(id, function(err, user) {
    if (err) { return error(err); }

    Twitter.get('/statuses/user_timeline.json', user.username, function(err, data) {
      if (err) { return error(err); }
      console.log(data);
    });
  });
});

function error(err) { console.error("Program derp:", err); process.exit(1); }

2-promises.js

// --------------------------------------------------------------------
// Let's try it Promises-style
// (a'la Q.js)

getUserID()
.then(function(id) {
  return User.find(id);
})
.then(function(user) {
  return Twitter.get('/statuses/user_timeline.json', user.username);
})
.then(function(timeline) {
  console.log(timeline);
})
.fail(function(err) {
  console.error("Derpity derp:", err);
  process.exit(1);
})

3-promises.coffee

// --------------------------------------------------------------------
// What does that look like in CoffeeScript?
// Much cleaner!

getUserID()
.then (id) ->
  User.find(id)

.then (user) ->
  Twitter.get('/statuses/user_timeline.json', user.username)

.then (timeline) ->
  console.log(timeline)

.fail (err) ->
  console.error("Derpity derp:", err)
  process.exit(1)