jsp测试函数的运行速度方法
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.uuid = uuid++;
}
document.getElementById("time-1").innerHTML = new Date() - time1;
var time2 = new Date();
var i = divs.length; while (--i >= 0) {
divs.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.uuid = uuid++;
}
document.getElementById("time-3").innerHTML = new Date() - time3;
var time4 = new Date();
for (var n = divs.length - 1; n >= 0; n--) {
divs.uuid = uuid++;
}
document.getElementById("time-4").innerHTML = new Date() - time4;
var time5 = new Date();
for (var n = divs.length - 1; n--;) {
divs.uuid = uuid++;
}
document.getElementById("time-5").innerHTML = new Date() - time5;
var time6 = new Date();
var n = divs.length-1; do {
divs.uuid = uuid++;
} while (n--);
document.getElementById("time-6").innerHTML = new Date() - time6;
var time7 = new Date();
for(var i=0,el;el = divs;){
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;){ } <span class="red">顺序</span></h2>
<p id="time-7"></p>
</body>
</html>
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https://www.uoften.com/program/jsp/20180413/48039.html
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