让getElementsByClassName兼容

function getElementsByClassName(node, classname){
    if(node.getElementsByClassName){
        //使用现有方法
        return node.getElementsByClassName(classname);
    }else{
        var results = nes Array();
        var elems = node.getElementsByTagName("*");
        for(var i=0; i<elems.length; i++){
            if(elems[i].className.indexOf(classname) != -1){
                results[results.length] = elems[i];
            }
        }
        return results;
    }
}