内存泄漏常见的原因有三种：
1. 闭包
2. 未解除事件绑定
3. 循环引用DOM元素
除此之外，还有一种泄漏原因少有人知，它和innerHTML有关，不过很容易解决。
出现这种内存泄漏需要有三个条件：
1. 内存中存在一个未加入DOM树的元素
2. 给这个元素设置innerHTML，注意，必须是能创建元素并且绑定了DOM 0级事件
3. 必须在这个元素加入DOM树前设置它的innerHTML
举个例子：
// 创建一个仅存在于内存中的元素var el = document.createElement('div');// 设置innerHTMLel.innerHTML = '<a onclick = "testFn()">Test Link</a>';// 加入DOM树document.body.appendChild(el) |
这种写法很常见对吧，但你根本察觉不到有内存泄漏。唯一的隐患在于，当你在一个相同的页面上频繁地用这种方式设置innerHTML，一次又一次，反反复复，没完没了，好吧，其实也没那么多次，总之是很多次之后，就会出现问题了。
肯定有人会说，谁那么蛋疼地总折腾一个元素，其实在ajax泛滥的时代，经常需要动态更新页面，所以这种情况也并非罕见。
如果实在不信，这里有两个DEMO页面:
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>IE innerHTML Memory Leak Demo</title>
<style type = "text/css">
html,body
{
font-family: arial;
font-size: 120%;
}
div a
{
font-size: 120%;
display: block;
margin: 5px;
padding: 5px;
border: 2px solid #000;
background-color: lightgreen;
}
</style>
<script type = "text/javascript">
var btnStart, btnStop;
function init()
{
btnStart = document.getElementById('btnStart');
btnStop = document.getElementById('btnStop');
btnStart.onclick = startLeak;
btnStop.onclick = stopLeak;
}
function startLeak()
{
btnStart.disabled = true;
btnStop.disabled = false;
leak();
}
function stopLeak()
{
btnStop.disabled = true;
btnStart.disabled = false;
}
function leak()
{
if (btnStop.disabled == true)
{
return;
}
var str = '';
var i, len = 2000;
for (i = 0; i < len; i++)
{
str += '<a onclick = "test()">Test Link</a>';
}
var elem = document.getElementById('testDiv');
if (elem) document.body.removeChild(elem);
var elem = document.createElement('div');
elem.id = 'testDiv';
// Oops! Setting .innerHTML first, and _then_ calling .appendChild(..) is asking for a memory leak!
elem.innerHTML = str;
document.body.appendChild(elem);
setTimeout(leak, 250);
}
function test()
{
alert('Click!');
return false;
}
window.onload = init;
</script>
</head>
<body>
<h1>IE innerHTML Memory Leak Demo</h1>
<p>Upon clicking the "Start Leak" button, a script will execute repeatedly which creates a new <div> element in memory,
sets its innerHTML to a string of 2000 <a> tags with onclick events wired up ('<a onclick = "test()">Test Link</a>'),
and then adds that <div> to the
page.</p>
<p>Letting this script run for about 60 seconds, and using Perfmon to monitor memory consumption, you should notice a significant
increase in the amount of memory consumed. To see the same script logic that doesn't leak memory, view the
<a href = "./noleak.html">No Leak Page</a>.</p>
<button id = "btnStart">Start Leak</button>
<button id = "btnStop" disabled = "disabled">Stop Leak</button>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>IE innerHTML Memory Leak Demo (the fix)</title>
<style type = "text/css">
html,body
{
font-family: arial;
font-size: 120%;
}
div a
{
font-size: 120%;
display: block;
margin: 5px;
padding: 5px;
border: 2px solid #000;
background-color: lightgreen;
}
</style>
<script type = "text/javascript">
var btnStart, btnStop;
function init()
{
btnStart = document.getElementById('btnStart');
btnStop = document.getElementById('btnStop');
btnStart.onclick = startLeak;
btnStop.onclick = stopLeak;
}
function startLeak()
{
btnStart.disabled = true;
btnStop.disabled = false;
leak();
}
function stopLeak()
{
btnStop.disabled = true;
btnStart.disabled = false;
}
function leak()
{
if (btnStop.disabled == true)
{
return;
}
var str = '';
var i, len = 2000;
for (i = 0; i < len; i++)
{
str += '<a onclick = "test()">Test Link</a>';
}
var elem = document.getElementById('testDiv');
if (elem) document.body.removeChild(elem);
var elem = document.createElement('div');
elem.id = 'testDiv';
// Add the element to the DOM first, and /then/ set .innerHTML to prevent memory from leaking.
document.body.appendChild(elem);
elem.innerHTML = str;
setTimeout(leak, 250);
}
function test()
{
alert('Click!');
return false;
}
window.onload = init;
</script>
</head>
<body>
<h1>IE innerHTML Memory Leak Demo (the fix)</h1>
<p>Upon clicking the "Start Leak" button, a script will execute repeatedly which creates a new <div> element in memory and
then adds that element to the page. Only <em>after</em> the element has been added to the page, do we set its .innerHTML to a
string to 2000 <a> tags with onclick events wired up ('<a onclick = "test()">Test Link</a>').</p>
<p>Letting this script run for about 60 seconds, and using Perfmon to monitor memory consumption, you should notice that,
unlike the <a href = "./leak.html">Leak Page</a>, memory consumption remains relatively constant.</p>
<button id = "btnStart">Start Leak</button>
<button id = "btnStop" disabled = "disabled">Stop Leak</button>
</body>
</html>
接着来看怎么解决它：
其实很简单，换个顺序，先把元素加入DOM树，再设置innerHTML。
当然你也可以完全放弃使用innerHTML，这样做好处多多，比如不会存在未解除事件绑定的情况，但貌似完全放弃innerHTML也不现实。。。