Callbacks vs Promises

gistfile1.coffee

#callbacks  
async.parallel([
  (done) ->
    Post.findAll((err, posts) ->
      done(err, posts)
    )
  (done) ->
    Category.findAll((err, docs) ->
      done(err, docs)
    )
  ],
  (err, results) ->
    if err 
      #do err stuff
    [posts, categories] = results
    #do stuff

#promises
Q.all([Post.findAll(), Category.findAll()])
  .then((results) ->
    [posts, categories] = results
    #do stuff
  ).fail((err) ->
    #do err stuff
  )