<!DOCTYPE html>
<html><head>
<meta charset="UTF-8"> <title></title> </head> <script type=" text/javascript"> function loop() { for (var i = 0; i <= 1000000; ++i){ document.write(""); } } (function() { var start = Date.now(); loop(); var end = Date.now(); var use = end - start; document.write("loop()花费时间：" + use + "毫秒"); })(); </script><body>
</body></html>
//检查loop()运行时间
loop()花费时间：165毫秒