Fix element when scrolled offscreen

scroll-fix.js

$(function(){
		
	var unfix_distance = $('nav#menu').offset().top,
		$fixed_element = $('nav#menu');
		
	window.onresize = function() {
		unfix_distance = $('nav#menu').offset().top;
	}
	
	$(window).scroll(function(){
		
		if( $fixed_element.offset().top - $(window).scrollTop() < 0 ){
			$fixed_element.addClass('fixed');
		}
		
		if( $(window).scrollTop() < unfix_distance ){
			$fixed_element.removeClass('fixed');
		}

	});

});