sticky scroll directive in coffeescript

sticky-scroll.coffee

appDirectives.directive 'stickyScroll', ->
  return {
    restrict: 'A'

    link: (scope, element, attr) ->
      unregisterWatch = scope.$watch(
        -> return element[0].scrollHeight,
        ->
          element[0].scrollTop = element[0].scrollHeight
      )
      element.on '$destroy', ->
        unregisterWatch()
  }