兼容ie下的getElementsByClassName

function getClassNames(classStr,tagName){
          if (document.getElementsByClassName) {
                return document.getElementsByClassName(classStr)
          }else {
                var nodes = document.getElementsByTagName(tagName),ret = [];         
                for(i = 0; i < nodes.length; i++) {
             if(hasClass(nodes[i],classStr)){
                    ret.push(nodes[i])
             }
          }
          return ret;
           }
    }
    function hasClass(tagStr,classStr){
         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
         for (var i=0;i