Navbar on scroll change

custom.js

(function($) {

	$(window).scroll(function() {

		var height = $(window).height();

	    if ($(window).scrollTop() / 2 > height) {
	        $('#header-nav').addClass('scrolled-navbar');
	        
	    }
	    else {
	        $('#header-nav').removeClass('scrolled-navbar');
	    }
	});

})(jQuery);