Fixed Directive

fixed.js

.directive('setClassWhenAtTop', function($window) {
	var $win = angular.element($window); // wrap window object as jQuery object

	return {
		restrict: 'A',
		link: function(scope, element, attrs) {
			var topClass = attrs.setClassWhenAtTop, // get CSS class from directive's attribute value
				offsetTop = element.offset().top; // get element's offset top relative to document

			$win.on('scroll', function(e) {
				if ($win.scrollTop() >= offsetTop) {
					element.addClass(topClass);
				} else {
					element.removeClass(topClass);
				}
			});
		}
	};
})