兼容IE8及以下的getElementsByClassName()方法

1  2     function getElementsByClassName = function(className, tagName) { 3         //如果浏览器支持getElementsByClassName()就直接返回 4         if(document.getElementsByClassName){ 5             return document.getElementsByClassName(className) 6         } 7         //否则遍历document文档指定的标签名集合 8         var children = document.getElementsByTagName(tagName); 9         //此数组用于保存遍历后得到的class元素10         var elements = new Array();11      12         for (var i = 0; i < children.length; i++) {13             var child = children[i];14             var classNames = child.className.split(' ');            //分割多个class元素15             for (var j = 0; j < classNames.length; j++) {16                 if (classNames[j] == className) {17                     elements.push(child);18                     break;19                 }20             }21         }22         return elements;23     };