Coffee Arrows

a.coffee

class SomeAjaxCallback
  constructor: (@value) ->
    throw "Bad value" unless value?
    setTimeout @process, 5000
  # setTimeout doesn't give us a "new context"
  # so we'd get our "global context" : window.
  # let's avoid that using the fat arrow.
  process: =>
    throw "Wrong context" unless @value?

class SomeElement
  constructor: (@value, sel) ->
    # now, we have another problem.
    # We need to keep our `this`, but
    # jQuery gives us a new one through the event.
    # Thankfully, we can use the parameter (ev)
    # to get the target, and still use the fat arrow.
    $(sel).click @onclick
  onclick: (ev) =>
    $(ev.target).html @value

class NotNiceApi
  constructor: (@value) ->
    # now, the third case :
    # the library doesn't pass the new `this`
    # as an argument. We have to bind
    # the function by ourselves.
    self = this
    onmsg = ->
      @dispatch 'new value', self.value
    SomeApi.on 'message', onmsg