在JavaScript中使用inline函数的问题
前段时间被IE和JavaScript脚本引擎的Memory Leak问题弄得郁闷坏了，不过幸好现在总算是柳暗花明了，并且找到了一些IE中使用脚本避免ML问题的方法。继续研究JavaScript的编写，有发现一些不算ML问题，但是可以节约IE内存使用的方法，在此和大家讨论讨论。
我们在JavaScript中编写代码，对于定义函数的语句：
function foo()
{
// TODO: . . .
return x;
}
var foo = function()
{
// TODO: . . .
return x;
}
var foo = new Function('{/*todo*/return x;}');
function TestObject.prototype.Render(doc, id)
{
var span = doc.createElement('SPAN');
span.Object = this;
this.m_Element = span;
if ( id == "NamedMethod" )
{
span.onclick = asdf;
}
else
{
span.onclick = function()
{
var asdf01 = ['a', 's', 'd', 'f'];
var asdf02 = ['a', 's', 'd', 'f'];
var asdf03 = ['a', 's', 'd', 'f'];
var asdf04 = ['a', 's', 'd', 'f'];
var asdf05 = ['a', 's', 'd', 'f'];
var asdf06 = ['a', 's', 'd', 'f'];
var asdf07 = ['a', 's', 'd', 'f'];
var asdf08 = ['a', 's', 'd', 'f'];
var asdf09 = ['a', 's', 'd', 'f'];
var asdf10 = ['a', 's', 'd', 'f'];
var asdf11 = ['a', 's', 'd', 'f'];
var asdf12 = ['a', 's', 'd', 'f'];
};
}
span.Name = this.m_Description;
span.innerText = this.m_Name;
span.style.display = 'block';
return span;
}
// IE消耗的内存数量（PM+VM）
单看绝对内存消耗差别不大，可是如果看相对内存消耗：(35.2-33.4)/(33.4-27.4) = 30% !!!，还是很可观的了，而且如果方法本省越大，inline时冗余数据就越多。
附测试代码：<html>
<head>
<title>JScript Function Spending</title>
<meta name="author" content="birdshome@博客园" />
</head>
<body onunload="ReleaseElements()">
<button id="NamedMethod" onclick="GenerateObjects(this)">
Append Normal Elements</button>
<button id="AnonymousMethod" onclick="GenerateObjects(this)">
Append Inline Elements</button>
<div id="container">
</div>
<script language="Javascript">
function GenerateObjects(elmt)
{
var room = document.getElementById('container');
for ( var i=0 ; i < 1000 ; ++i )
{
var obj = new TestObject('__Object__' + i);
room.appendChild(obj.Render(document, elmt.id));
}
}
function TestObject(name)
{
this.m_Name = name;
this.m_Description = '';
this.m_Element = null;
this.toString = function()
{
return '[class TestObject]';
}
}
function TestObject.prototype.Render(doc, id)
{
var span = doc.createElement('SPAN');
span.Object = this;
this.m_Element = span;
if ( id == "NamedMethod" )
{
span.onclick = asdf;
}
else
{
span.onclick = function()
{
var asdf01 = ['a', 's', 'd', 'f'];
var asdf02 = ['a', 's', 'd', 'f'];
var asdf03 = ['a', 's', 'd', 'f'];
var asdf04 = ['a', 's', 'd', 'f'];
var asdf05 = ['a', 's', 'd', 'f'];
var asdf06 = ['a', 's', 'd', 'f'];
var asdf07 = ['a', 's', 'd', 'f'];
var asdf08 = ['a', 's', 'd', 'f'];
var asdf09 = ['a', 's', 'd', 'f'];
var asdf10 = ['a', 's', 'd', 'f'];
var asdf11 = ['a', 's', 'd', 'f'];
var asdf12 = ['a', 's', 'd', 'f'];
};
}
span.Name = this.m_Description;
span.innerText = this.m_Name;
span.style.display = 'block';
return span;
}
function asdf()
{
var asdf01 = ['a'
, 's', 'd', 'f'];
var asdf02 = ['a', 's', 'd', 'f'];
var asdf03 = ['a', 's', 'd', 'f'];
var asdf04 = ['a', 's', 'd', 'f'];
var asdf05 = ['a', 's', 'd', 'f'];
var asdf06 = ['a', 's', 'd', 'f'];
var asdf07 = ['a', 's', 'd', 'f'];
var asdf08 = ['a', 's', 'd', 'f'];
var asdf09 = ['a', 's', 'd', 'f'];
var asdf10 = ['a', 's', 'd', 'f'];
var asdf11 = ['a', 's', 'd', 'f'];
var asdf12 = ['a', 's', 'd', 'f'];
}
</script>
<script language="javascript">
function ReleaseElements()
{
var room = document.getElementById('container');
var spans = room.all.tags('SPAN');
for ( var i=0 ; i < spans.length ; ++i )
{
spans[i].Object = '';
}
}
</script>
</body>
</html>
我们在JavaScript中编写代码，对于定义函数的语句：
function foo(){ // TODO: . . . return x;}
可以说是在熟悉不过了。当然除了这种定义函数的方法，我们还有另外几种方法也能定义函数：
var foo = function(){ // TODO: . . . return x;}var foo = new Function('{/*todo*/return x;}');
后两种方法定义的JavaScript函数，在调用起来和第一种没有任何效果上的区别。
不过由于JavaScript是解释性语言，当我们定义一个函数的时候，解析引擎生成一个Function对象实例，然后把函数内容保存下来。所以每执行一次函数定义语句，就会生成一个函数。而不像编译语言，一个函数编译一次后就被任何语句调用。啊？难道JavaScript不能调用定义好的函数？不是这个意思了，当我们在制作JavaScript控件时，如果动态输出DHTML来作为控件的内容，就容易出现这样的问题。比如我们在一个HTML对象生成过程中，使用了inline方式定义的函数，那么这个元素生成几次，那个函数也就要同时生成几次。
function TestObject.prototype.Render(doc, id) { var span = doc.createElement('SPAN'); span.Object = this; this.m_Element = span; if ( id == "NamedMethod" ) { span.onclick = asdf; } else { span.onclick = function() { var asdf01 = ['a', 's', 'd', 'f']; var asdf02 = ['a', 's', 'd', 'f']; var asdf03 = ['a', 's', 'd', 'f']; var asdf04 = ['a', 's', 'd', 'f']; var asdf05 = ['a', 's', 'd', 'f']; var asdf06 = ['a', 's', 'd', 'f']; var asdf07 = ['a', 's', 'd', 'f']; var asdf08 = ['a', 's', 'd', 'f']; var asdf09 = ['a', 's', 'd', 'f']; var asdf10 = ['a', 's', 'd', 'f']; var asdf11 = ['a', 's', 'd', 'f']; var asdf12 = ['a', 's', 'd', 'f']; }; } span.Name = this.m_Description; span.innerText = this.m_Name; span.style.display = 'block'; return span; }
函数span.onclick = function()中的内容是用来占位置的，这样inline方式定义函数，每次Render()都就会生成一个新的函数对象。使用inline方式有什么不好呢？当对象实例多了的时候，会很明显的浪费内存空间呀，试验数据如下：
| Normal Method | Inline Method | |
|---|---|---|
| Initialized | 27.4 M | 27.4 M |
| Rendered | 33.4 M | 35.2 M |
// IE消耗的内存数量（PM+VM）
单看绝对内存消耗差别不大，可是如果看相对内存消耗：(35.2-33.4)/(33.4-27.4) = 30% !!!，还是很可观的了，而且如果方法本省越大，inline时冗余数据就越多。
附测试代码：
<html><head> <title>JScript Function Spending</title> <meta name="author" content="birdshome@博客园" /> </head><body onunload="ReleaseElements()"> <button id="NamedMethod" onclick="GenerateObjects(this)"> Append Normal Elements</button> <button id="AnonymousMethod" onclick="GenerateObjects(this)"> Append Inline Elements</button> <div id="container"> </div> <script language="Javascript">function GenerateObjects(elmt){ var room = document.getElementById('container'); for ( var i=0 ; i < 1000 ; ++i ) { var obj = new TestObject('__Object__' + i); room.appendChild(obj.Render(document, elmt.id)); } }function TestObject(name){ this.m_Name = name; this.m_Description = ''; this.m_Element = null; this.toString = function() { return '[class TestObject]'; }}function TestObject.prototype.Render(doc, id){ var span = doc.createElement('SPAN'); span.Object = this; this.m_Element = span; if ( id == "NamedMethod" ) { span.onclick = asdf; } else { span.onclick = function() { var asdf01 = ['a', 's', 'd', 'f']; var asdf02 = ['a', 's', 'd', 'f']; var asdf03 = ['a', 's', 'd', 'f']; var asdf04 = ['a', 's', 'd', 'f']; var asdf05 = ['a', 's', 'd', 'f']; var asdf06 = ['a', 's', 'd', 'f']; var asdf07 = ['a', 's', 'd', 'f']; var asdf08 = ['a', 's', 'd', 'f']; var asdf09 = ['a', 's', 'd', 'f']; var asdf10 = ['a', 's', 'd', 'f']; var asdf11 = ['a', 's', 'd', 'f']; var asdf12 = ['a', 's', 'd', 'f']; }; } span.Name = this.m_Description; span.innerText = this.m_Name; span.style.display = 'block'; return span;}function asdf(){ var asdf01 = ['a'
, 's', 'd', 'f']; var asdf02 = ['a', 's', 'd', 'f']; var asdf03 = ['a', 's', 'd', 'f']; var asdf04 = ['a', 's', 'd', 'f']; var asdf05 = ['a', 's', 'd', 'f']; var asdf06 = ['a', 's', 'd', 'f']; var asdf07 = ['a', 's', 'd', 'f']; var asdf08 = ['a', 's', 'd', 'f']; var asdf09 = ['a', 's', 'd', 'f']; var asdf10 = ['a', 's', 'd', 'f']; var asdf11 = ['a', 's', 'd', 'f']; var asdf12 = ['a', 's', 'd', 'f'];}</script> <script language="javascript">function ReleaseElements(){ var room = document.getElementById('container'); var spans = room.all.tags('SPAN'); for ( var i=0 ; i < spans.length ; ++i ) { spans[i].Object = ''; }} </script></body></html>
