http://alloyteam.github.io/CodeGuide/javascripts/jquery_scrolltotop.js

1/*!
2    jQuery scrollTopTop v1.0 - 2013-03-15
3    (c) 2013 Yang Zhao - geniuscarrier.com
4    license: http://www.opensource.org/licenses/mit-license.php
5*/
6(function($) {
7    $.fn.scrollToTop = function(options) {
8        var config = {
9            "speed" : 400
10        };
11
12        if (options) {
13            $.extend(config, {
14                "speed" : options
15            });
16        }
17
18        return this.each(function() {
19
20            var $this = $(this);
21
22            $(window).scroll(function() {
23                if ($(this).scrollTop() > 100) {
24                    $this.fadeIn();
25                } else {
26                    $this.fadeOut();
27                }
28            });
29
30            $this.click(function(e) {
31                e.preventDefault();
32                $("body, html").animate({
33                    scrollTop : 600
34                }, config.speed);
35            });
36
37        });
38    };
39})(jQuery);