Angular directive for scroll spy

directive_scrollSpy

'use strict';

angular.module('AppSuccess')
  .directive('scrollSpy', ['$window', function ($window) {
    return {
      restrict: 'A',
      link: function (scope, element) {

        // Get offset before scrollSpy activates
        // otherwise offset of element would change
        var elmOffset = $(element).offset().top;

        // Track if window scroll passes element offset
        var scrollSpy = function() {
          var windowScroll = $window.scrollY;
          if ( windowScroll > elmOffset ) {
            element.addClass('sticky');
          } else {
            element.removeClass('sticky');
          }
        };

        // Throttled so it doesn't fire all the time
        var throttledScrollSpy = _.throttle(scrollSpy, 100);
        angular.element($window).bind('scroll', throttledScrollSpy);
      }
    };
  }]);