https://www.afaindia.com/vendor/jquery.appear.js

1/*
2 * jQuery.appear
3 * https://github.com/bas2k/jquery.appear/
4 * http://code.google.com/p/jquery-appear/
5 * http://bas2k.ru/
6 *
7 * Copyright (c) 2009 Michael Hixson
8 * Copyright (c) 2012-2014 Alexander Brovikov
9 * Licensed under the MIT license (http://www.opensource.org/licenses/mit-license.php)
10 */
11(function($) {
12    $.fn.appear = function(fn, options) {
13        var settings = $.extend({
14
15            data: undefined,
16
17            one: true,
18            accX: 0,
19            accY: 0
20
21        }, options);
22
23        return this.each(function() {
24            var t = $(this);
25            t.appeared = false;
26            if (!fn) {
27                t.trigger('appear', settings.data);
28                return;
29            }
30            var w = $(window);
31            var check = function() {
32                if (!t.is(':visible')) {
33                    t.appeared = false;
34                    return;
35                }
36
37                var a = w.scrollLeft();
38                var b = w.scrollTop();
39                var o = t.offset();
40                var x = o.left;
41                var y = o.top;
42
43                var ax = settings.accX;
44                var ay = settings.accY;
45                var th = t.height();
46                var wh = w.height();
47                var tw = t.width();
48                var ww = w.width();
49
50                if (y + th + ay >= b &&
51                    y <= b + wh + ay &&
52                    x + tw + ax >= a &&
53                    x <= a + ww + ax) {
54                    if (!t.appeared) t.trigger('appear', settings.data);
55                } else {
56                    t.appeared = false;
57                }
58            };
59           var modifiedFn = function() {
60                t.appeared = true;
61                if (settings.one) {
62                    w.unbind('scroll', check);
63                    var i = $.inArray(check, $.fn.appear.checks);
64                    if (i >= 0) $.fn.appear.checks.splice(i, 1);
65                }
66                fn.apply(this, arguments);
67            };
68
69            if (settings.one) t.one('appear', settings.data, modifiedFn);
70            else t.bind('appear', settings.data, modifiedFn);
71            w.scroll(check);
72            $.fn.appear.checks.push(check);
73            (check)();
74        });
75    };
76
77    $.extend($.fn.appear, {
78
79        checks: [],
80        timeout: null,
81
82        checkAll: function() {
83            var length = $.fn.appear.checks.length;
84            if (length > 0) while (length--) ($.fn.appear.checks[length])();
85        },
86        run: function() {
87            if ($.fn.appear.timeout) clearTimeout($.fn.appear.timeout);
88            $.fn.appear.timeout = setTimeout($.fn.appear.checkAll, 20);
89        }
90    });
91    $.each(['append', 'prepend', 'after', 'before', 'attr',
92        'removeAttr', 'addClass', 'removeClass', 'toggleClass',
93        'remove', 'css', 'show', 'hide'], function(i, n) {
94        var old = $.fn[n];
95        if (old) {
96            $.fn[n] = function() {
97                var r = old.apply(this, arguments);
98                $.fn.appear.run();
99                return r;
100            }
101        }
102    });
103
104})(jQuery);