From http://hi.baidu.com/562127378/item/3b492a01fd95d0c9915718eb

让所有的浏览器都支持 getElementsByClassName.js

var getElementsByClassName = function (searchClass, node,tag) {
  if(document.getElementsByClassName){
       var nodes =  (node || document).getElementsByClassName(searchClass),result = [];
            for(var i=0 ;node = nodes[i++];){
              if(tag !== "*" && node.tagName === tag.toUpperCase()){
                   result.push(node)
              }
            }
            return result
       }else{
            node = node || document;
            tag = tag || "*";
            var classes = searchClass.split(" "),
            elements = (tag === "*" && node.all)? node.all : node.getElementsByTagName(tag),
            patterns = [],
            current,
            match;
            var i = classes.length;
            while(--i >= 0){
              patterns.push(new RegExp("(^|\\s)" + classes[i] + "(\\s|$)"));
            }
            var j = elements.length;
            while(--j >= 0){
              current = elements[j];
              match = false;
              for(var k=0, kl=patterns.length; k<kl; k++){
                   match = patterns[k].test(current.className);
                   if (!match)  break;
              }
              if (match)  result.push(current);
            }
            return result;
       }
  }