var num = 10000for (var i = 0; i++; i < num) {    eval("pp" + i + "=" + i);}(function(window, undefined){    var a1 = new Date();    for (var i = 0; i < num; i++) {        document.write(window["pp" + i]);    }    var a2 = new Date();    alert(a2.getTime() - a1.getTime());})(window);(function(undefined){    var a1 = new Date();    for (var i = 0; i < num; i++) {        document.write(window["pp" + i]);    }    var a2 = new Date();    alert(a2.getTime() - a1.getTime());})();

速度提升2/3

来自：http://blog.csdn.net/qq1119753812/article/details/6820697

PS：在一间屋子里找一个杯子，和在茶几上找一个杯子；