jsp测试函数的运行速度方法

2020-07-27 21:26:26

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通常我们需要对函数进行优化，一般的做法是开始的时候获得时间，结束的时候再获得一次时间，两次时间相减就能到到花费的时间。而函数运行速度之快，基本上都是毫秒级的。

下面给出的函数就是就此准备的。

// 时间转为时间戳（毫秒）function time2stamp(){  var d = new Date();  return Date.parse(d)+d.getMilliseconds();}

用法：

var t1 = time2stamp();// 比较各游览器的DOM运行速度。var divs = document.getElementByTagName("div"); var t2 = time2stamp();alert("耗时：" + (t2 - t1) + " 毫秒");

新的方法:

var time1 = new Date// 比较各游览器的DOM运行速度。var divs = document.getElementByTagName("div"); alert("耗时：" + (new Date - time1) + " 毫秒");

测试各种循环的效率，for...in这样慢的循环就不测了！

<!doctype html><html dir="ltr" lang="zh-CN"> <head>  <meta charset="utf-8"/>  <title>类</title>  <script type="text/javascript" charset="utf-8">   window.onload = function(){     for (var i=0, elm; i<4000; i++) {     elm = document.createElement("div");     elm.innerHTML = "第一重div<div>第二重div<div>第三重div</div></div>";     document.body.appendChild(elm);    }    document.getElementById("start-test").onclick = startTest;    var uuid = 0;    function startTest() {     var divs = document.getElementsByTagName("div");      var time1 = new Date();     var i = -1, n = divs.length;while (++i < n) {        divs[i].uuid = uuid++;     }     document.getElementById("time-1").innerHTML = new Date() - time1;      var time2 = new Date();     var i = divs.length; while (--i >= 0) {       divs[i].uuid = uuid++;     }      document.getElementById("time-2").innerHTML = new Date() - time2;      var time3 = new Date();     for (var i=0, n=divs.length; i<n; i++) {       divs[i].uuid = uuid++;     }     document.getElementById("time-3").innerHTML = new Date() - time3;       var time4 = new Date();     for (var n = divs.length - 1; n >= 0; n--) {        divs[n].uuid = uuid++;      }     document.getElementById("time-4").innerHTML = new Date() - time4;      var time5 = new Date();     for (var n = divs.length - 1; n--;) {        divs[n].uuid = uuid++;      }     document.getElementById("time-5").innerHTML = new Date() - time5;      var time6 = new Date();     var n = divs.length-1; do {        divs[n].uuid = uuid++;     } while (n--);     document.getElementById("time-6").innerHTML = new Date() - time6;     var time7 = new Date();     for(var i=0,el;el = divs[i++];){      el.uuid = uuid++;     };     document.getElementById("time-7").innerHTML = new Date() - time7;     }   }  </script> </head> <body>  <style>   h2 {    margin:0;    padding:10px;    font-weight:500;    font-size:13px;    background:#8080C0;    color:#fff;   }   p {    margin:0;    text-indent:2em;    border-bottom:2px solid #a9ea00;    background:#F2F1D7;   }   span.red{    color:red;   }  </style>  <h1>JavaScript loop speed test</h1>  <ul>   <li>遍历页面上12000个DIV</li>  </ul>  <input id="start-test" type="button" value="Start test">  <h2>循环1： var i = -1, n = divs.length;while (++i < n) { }<span class="red">顺序</span></h2>  <p id="time-1"></p>   <h2>循环2：var n = divs.length; while (--n >= 0) { }<span class="red">倒序</span></h2>  <p id="time-2"></p>   <h2>循环3：for (var i=0, n=divs.length; i<n; i++)<span class="red">顺序</span></h2>  <p id="time-3"></p>   <h2>循环4：for (var n = divs.length - 1; n >= 0; n--) { }<span class="red">倒序</span></h2>  <p id="time-4"></p>   <h2>循环5：for (var n = divs.length - 1; n--;) { }<span class="red">倒序</span></h2>  <p id="time-5"></p>   <h2>循环6： var n = divs.length-1; do { } while (n--)<span class="red">倒序</span></h2>  <p id="time-6"></p>  <h2>循环7： for(var i=0,el;el = divs[i++];){ } <span class="red">顺序</span></h2>  <p id="time-7"></p> </body></html>

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