AngularJS directive for affixing elements

affix.js

angular.module('affix', []).directive('affix', [function () {
        return {
            restrict: 'A',
            scope: {offset: "="},
            link: function (scope, element, attrs) {
                var offset = Number.isFinite(scope.offset) ? scope.offset : 300;
                var onScroll = function () {
                    if (window.pageYOffset >= offset) {
                        element.addClass('affix'); // add affix class
                    } else {
                        element.removeClass('affix'); // remove affix class
                    }
                };
                window.onscroll = onScroll;
                scope.$on('$destroy', function () {
                    window.onscroll = angular.noop;
                });
            }
        };
    }]);