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Problems using inline functions in JavaScript_javascript tips

WBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOriginal: 2016-05-16 19:17:541373browse

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()
Problems using inline functions in JavaScript_javascript tips

{

// TODO: . . .
Problems using inline functions in JavaScript_javascript tips

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()
Problems using inline functions in JavaScript_javascript tips

{

// TODO: . . .
Problems using inline functions in JavaScript_javascript tips

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)
Problems using inline functions in JavaScript_javascript tips

{

var span = doc.createElement('SPAN');
Problems using inline functions in JavaScript_javascript tips

span.Object = this;
Problems using inline functions in JavaScript_javascript tips

this.m_Element = span;
Problems using inline functions in JavaScript_javascript tips

if ( id == "NamedMethod" )
Problems using inline functions in JavaScript_javascript tips

{

span.onclick = asdf;
Problems using inline functions in JavaScript_javascript tips

}

else

{

span.onclick = function()
Problems using inline functions in JavaScript_javascript tips

{

var asdf01 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf02 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf03 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf04 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf05 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf06 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf07 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf08 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf09 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf10 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf11 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

var asdf12 = ['a', 's', 'd', 'f'];
Problems using inline functions in JavaScript_javascript tips

};

}

span.Name = this.m_Description;
Problems using inline functions in JavaScript_javascript tips

span.innerText = this.m_Name;
Problems using inline functions in JavaScript_javascript tips

span.style.display = 'block';
Problems using inline functions in JavaScript_javascript tips

return span;
Problems using inline functions in JavaScript_javascript tips

}

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

// Amount of memory consumed by IE (PM VM)

There is not much difference in absolute memory consumption alone, but if you look at relative memory consumption: (35.2 -33.4)/(33.4-27.4) = 30% !!!, which is still very impressive, and the larger the method itself, the more redundant data will be inline.

附测试代码：

<html>

<head>

<title>JScript Function Spendingtitle>
Problems using inline functions in JavaScript_javascript tips

head>

<body onunload="ReleaseElements()">
Problems using inline functions in JavaScript_javascript tips

<button id="NamedMethod" onclick="GenerateObjects(this)">
Problems using inline functions in JavaScript_javascript tips

Append Normal Elementsbutton>
Problems using inline functions in JavaScript_javascript tips

<button id="AnonymousMethod" onclick="GenerateObjects(this)">
Problems using inline functions in JavaScript_javascript tips

Append Inline Elementsbutton>
Problems using inline functions in JavaScript_javascript tips

<div id="container">
Problems using inline functions in JavaScript_javascript tips

div>

function GenerateObjects(elmt)
Problems using inline functions in JavaScript_javascript tips

{

var room = document.getElementById('container');
Problems using inline functions in JavaScript_javascript tips

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>

function ReleaseElements()
Problems using inline functions in JavaScript_javascript tips

{

var room = document.getElementById('container');
Problems using inline functions in JavaScript_javascript tips

var spans = room.all.tags('SPAN');
Problems using inline functions in JavaScript_javascript tips

for ( var i=0 ; i < spans.length ; ++i )

{

spans[i].Object = '';

}

script>

body>

html>

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