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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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标签:
javascript,函数,测试函数运行时间,js测试函数运行时间

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