1 (function($) {
 2     $.fn.scrollto = function(options) {
 3         // 将用户传递的参数去覆盖默认的参数然后返回一个新的对象
 4         this.opts = $.extend({}, $.fn.scrollto.defaults, options);
 5         console.log(this);
 6         return this.each(function() {
 7             $this = $(this);
 8             // $this.fadeOut();
 9             console.log($this);
10             $root = $('html,body');
11             console.log($root);
12             var opts = $.extend({}, $.fn.scrollto.defaults, options);
13             console.log(opts);
14             // checkpos($this,opts);
15 
16             $(window).on('scroll', checkpos($this, opts));
17 
18             if (opts.mode == 'move') {
19                 $this.on("click", move(opts));
20             } else {
21                 $this.on("click", go(opts));
22             }
23 
24         });
25 
26 
27 
28     };
29 
30     // private function
31     function checkpos(obj, opts) {
32         console.log($(window).scrollTop());
33         // document.title=$(window).scrollTop();
34         if ($(window).scrollTop() > opts.pos) {
35             obj.fadeIn();
36         } else {
37             obj.fadeOut();
38         }
39     }
40 
41 
42     // private function
43     function move(opts) {
44         console.log(this);
45         // var opts = this.opts,
46         //     dest = opts.dest;
47         if ($(window).scrollTop() !== opts.dest) {
48             if (!this.$root.is(':animated')) {
49                 $root.animate({
50                     scrollTop: opts.dest
51                 }, opts.speed);
52             }
53         }
54     }
55 
56     // paivate function
57     function go(opts) {
58         console.log(this);
59         var dest = opts.dest;
60         if ($(window).scrollTop() != dest) {
61             $root.animate({
62                 scrollTop: dest,
63             });
64         }
65     }
66 
67     $.fn.scrollto.defaults = {
68         pos: $(window).height(),
69         dest: 0,
70         speed: 800,
71         mode: 'move'
72     };
73 })(jQuery);
74 
75 
76 $("#backTop").scrollto({
77     mode: 'move'
78 });