重写setTimeout扩展参数

//判断函数行参长度来决定是否需要重写setTimeout，ie8以下为undefined
if(window.setTimeout.length == undefined){
    var __sto = window.setTimeout;
    window.setTimeout = function(callback,timeout,param){
        var args = Array.prototype.slice.call(arguments,2);
        __sto(function(){
            callback.apply(null,args);
        },timeout);
    };
}