How can one tell well written angular app? When he sees this and it's still ~60fps on a decent laptop

dont-try-this-at-home.js

$($window).on('scroll', function () {
    scope.$apply(function () {
        if ($window.pageYOffset > offsetTop) {
            elem.css('left', offsetLeft + 'px');
            elem.css('width', width + 'px')

            // position: fixed; top: 100px;
            elem.addClass('sticky');
        } else {
            elem.removeClass('sticky');
            elem.css('left', '');
            elem.css('width', '');
        }
    })
});