监听浏览器使用不同版本js并且处理ie兼容getElementByClassName

if(window.addEventListener){
    document.write('<script src="js/jquery-2.1.4.min.js"></script>');

}else if(window.attachEvent){
    document.write('<script src="js/jquery-1.8.3.min.js"></script>');
    //解决ie兼容getElementByClassName
    if(!document.getElementsByClassName){
        document.getElementsByClassName = function(className, element){
            var children = (element || document).getElementsByTagName('*');
            var elements = new Array();
            for (var i=0; i<children.length; i++){
                var child = children[i];
                var classNames = child.className.split(' ');
                for (var j=0; j<classNames.length; j++){
                    if (classNames[j] == className){
                        elements.push(child);
                        break;
                    }
                }
            }


            return elements;
        };
    }
    //


}else{
    document.write('<script src="js/jquery-2.1.4.min.js"></script>');
}