Example for a friend on how to use jQuery Deferreds

jquery-deferred-pattern.coffee

doSomething: ->
  d = jQuery.Deferred()

  doTheWork: ->
    data = hard()
    d.resolve(data)
    
  # return a promise which has a subset of the methods on a deferred
  # a promise won't allow you to cancel the deferred for example
  d.promise() 
  
p = doSomething() # get the promise

# now setup the callbacks
p.done (data) ->
  console.log 'Yay done!', data
  
p.fail ->
  console.log 'uh oh!'
  
# example of waiting on multiple promises
$.when.apply(this, promises).done -> console.log 'all done', arguments
  
  

A better explanation http://www.youtube.com/watch?v=HPb6e6EscEM