如何使用jsp测试函数的运行速度?

如何使用jsp测试函数的运行速度?

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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