IE8以下不支持getElementsByClassName方法

 1 function getElementsByClassName(classStr,tagName,element){
 2     tagName = (tagName || ‘*‘);
 3     element = (element || document);
 4     
 5     if(typeof tagName == ‘object‘){
 6         element = tagName; tagName = ‘*‘;
 7     }
 8     
 9     if(document.getElementsByClassName){
10         return element.getElementsByClassName(classStr);
11     }else{
12         var nodes = element.getElementsByTagName(tagName),
13             ret = [];
14         for(i = 0; i < nodes.length; i++) {
15             if(hasClass(nodes[i],classStr)) ret.push(nodes[i]);
16         }
17         return ret;
18     }
19 
20     function hasClass(tagStr,classStr){
21         var arr=tagStr.className.split(/\s+/ ); //这个正则表达式是因为class可以有多个,判断是否包含
22         for (var i=0;i<arr.length;i++){
23             if (arr[i]==classStr) return true;
24         }
25         return false;
26     };
27 };