Angular scroll directive

scrollDirective.coffee

# Updates a variable when the window scrollTop position is changed.
# Usage:
#   <set-window-scroll set-variable="windowScroll"></set-window-scroll>
app.directive "setWindowScroll", ->
  restrict: "E"
  scope:
    setVariable: "="

  link: (scope) ->
    $(window).scroll ->
      # Need to call $apply here since we are changing the scope *asynchronously* (in scroll callback).
      # See http://www.bennadel.com/blog/2449-Directive-Link-observe-And-watch-Functions-Execute-Inside-An-AngularJS-Context.htm

      scope.$apply ->
        scope.setVariable = $(window).scrollTop()

throttledScrollDirective.coffee

# Updates a variable when the window scrollTop position is changed.
# Usage:
#   <set-window-scroll set-variable="windowScroll"></set-window-scroll>
app.directive "setWindowScroll", ->
  restrict: "E"
  scope:
    setVariable: "="

  link: (scope) ->
    # Throttle to 300ms so that we don't call $apply so often.
    throttled = _.throttle ->
      scope.$apply ->
        scope.setVariable = $(window).scrollTop()
    , 300
    $(window).scroll throttled