Proportionate fade on scroll

fade.js

( function ( $, document ) {
  var fadeItem = function () {
		$('.fader').first().each( function() {
			var $this = $(this),
				$container = $this.parents( '.container' ),
				height_percentage = $container.height() / $( document ).height(),
				container_offset = $container.offset(),
				scroll_percent = $(window).scrollTop() / ($(document).height() - $(window).height() + container_offset.top);

			if ( $this.hasClass( 'is_stuck' )) {
				$this.css('opacity', 1 - (scroll_percent * height_percentage * 1.5));
			}
		});
	};

	var scrollDebounce = _.debounce(fadeItem, 100);
	var scrollThrottle = _.throttle(fadeItem, 100);
	
	$document.ready( function () {
	  
		$(window).scroll(function(){
			scrollDebounce();
			scrollThrottle();
		});

	});
} )( jQuery, document );