网页前端开发，对于图片慢加载简介

 1 //高度计算函数
 2 TestWeb.LayoutScroll = function (config) {
 3 
 4     var me = this;
 5     var defaults = {
 6         //参数
 7         box: null,
 8         isGoo: false,
 9         //初始化
10         init: function () {
11             //是否为ie，并读出ie版本
12             me.isIE = !!navigator.userAgent.match(/MSIE\b\s*([0-9]\.[0-9]);/img);
13             me.isIE && (me.isIE = RegExp.$1);
14             me.isGoo = !!navigator.userAgent.match(/AppleWebKit\b/img);
15             me.box = me.isIE ? document.documentElement : document;
16             me.bind();
17         },
18 
19         bind: function () {
20             me.box.onscroll = function () {
21                 //读取滚动条的位置和浏览器窗口的显示大小
22                 var top = me.isGoo ? document.body.scrollTop : document.documentElement.scrollTop,
23                     left = me.isGoo ? document.body.scrollLeft : document.documentElement.scrollLeft,
24                     width = document.documentElement.clientWidth,
25                     height = document.documentElement.clientHeight;
26            
27                 var lookHeight = top + height;
28 
29 
30                
31 
32                 var headerH = 120;
33                 var textH = 300;
34                 var imageH = 300;
35 
36 
37                 //计算出高度进行src替换
38                 if (lookHeight > (headerH + textH + imageH + 600)) {
39 
40 
41                     $("#ImageList2 img").each(function () {
42                         var src = $(this).attr("_src");
43 
44                         $(this).attr("src", src);
45                     });
46 
47                 }
48 
49                 //计算出高度进行src替换
50                 if (lookHeight > (headerH + (textH + imageH) * 2) + 600) {
51                     $("#ImageList3 img").each(function () {
52                         var src = $(this).attr("_src");
53 
54                         $(this).attr("src", src);
55                     });
56                 }
57 
58                 //计算出高度进行src替换
59                 if (lookHeight > (headerH + (textH + imageH) * 3) + 600) {
60                     $("#ImageList4 img").each(function () {
61                         var src = $(this).attr("_src");
62 
63                         $(this).attr("src", src);
64                     });
65                 }
66             }
67         }
68     };
69 
70     TestWeb.apply(me, config, defaults);
71     me.init();  //init
72 
73 }