https://www.sharpusa.com/Portals/_default/skins/www-usa/js/jquery.visible.js

1(function($) {
2
3  /**
4   * Copyright 2012, Digital Fusion
5   * Licensed under the MIT license.
6   * http://teamdf.com/jquery-plugins/license/
7   *
8   * @author Sam Sehnert
9   * @desc A small plugin that checks whether elements are within
10   *     the user visible viewport of a web browser.
11   *     only accounts for vertical position, not horizontal.
12   */
13
14   $.fn.visible = function(partial) {
15
16   	var $t            = $(this),
17   	$w            = $(window),
18   	viewTop       = $w.scrollTop(),
19   	viewBottom    = viewTop + $w.height(),
20   	_top          = $t.offset().top,
21   	_bottom       = _top + $t.height(),
22   	compareTop    = partial === true ? _bottom : _top,
23   	compareBottom = partial === true ? _top : _bottom;
24
25   	if($t.hasClass('visible')){
26   		return false;
27   	}
28
29   	return ((compareBottom <= viewBottom) && (compareTop >= viewTop));
30
31   };
32
33   var addAnimation = function(element){
34   	$(element).each(function(i, el){
35   		var el = $(el);
36   		if (el.visible(true)) {
37   			el.removeClass('visible').addClass('animated'); 
38   		} 
39   	});
40   }
41
42   var checkVisible = function(element){
43   	$(element).each(function(i, el) {
44   		var el = $(el);
45         if (el.visible(false)) {
46   			el.addClass("visible"); 
47   		} 
48   	});   	
49   }
50
51   $(window).load(function(){
52   	checkVisible('.animation');
53   });
54
55   $(window).scroll(function(event) {
56	  addAnimation('.animation');
57    });
58
59})(jQuery);