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在JavaScript中使用inline函数的问题

时间：2022-08-27 20:59 编辑：来源：阅读：
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摘要：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[url=http://www.cnblogs.com/birdshome/archive/2005/02/16/104967.html]柳暗花明[/url]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：

[img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] function foo() [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] // TODO: . . . [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] return x; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] }

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：

[img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var foo = function() [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] // TODO: . . . [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] return x; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] }

[img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] 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[b]内容[/b]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。

[img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] function TestObject.prototype.Render(doc, id) [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var span = doc.createElement('SPAN'); [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.Object = this; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] this.m_Element = span; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] if ( id == "NamedMethod" ) [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.onclick = asdf; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] else [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.onclick = function() [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf01 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf02 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf03 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf04 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf05 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf06 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf07 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf08 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf09 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf10 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf11 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] var asdf12 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] }; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.Name = this.m_Description; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.innerText = this.m_Name; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] span.style.display = 'block'; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] return span; [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] }

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

[i] // IE消耗的内存数量（PM+VM） [/i] 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) =[b]30% [/b]!!!，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：

[img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <html> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <head> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <title>JScript Function Spending</title> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <meta name="author" content="birdshome@博客园" /> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </head> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <body onunload="ReleaseElements()"> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <button id="NamedMethod" onclick="GenerateObjects(this)"> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] Append Normal Elements</button> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <button id="AnonymousMethod" onclick="GenerateObjects(this)"> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] Append Inline Elements</button> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] <div id="container"> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </div> [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedBlock.gif[/img] <script language="Javascript"> [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] function GenerateObjects(elmt) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var room = document.getElementById('container'); [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] for ( var i=0 ; i < 1000 ; ++i ) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var obj = new TestObject('__Object__' + i); [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] room.appendChild(obj.Render(document, elmt.id)); [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] function TestObject(name) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] this.m_Name = name; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] this.m_Description = ''; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] this.m_Element = null; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] this.toString = function() [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] return '[class TestObject]'; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] function TestObject.prototype.Render(doc, id) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var span = doc.createElement('SPAN'); [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.Object = this; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] this.m_Element = span; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] if ( id == "NamedMethod" ) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.onclick = asdf; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] else [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.onclick = function() [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf01 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf02 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf03 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf04 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf05 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf06 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf07 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf08 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf09 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf10 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf11 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf12 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] }; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.Name = this.m_Description; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.innerText = this.m_Name; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] span.style.display = 'block'; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] return span; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] function asdf() [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf01 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf02 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf03 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf04 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf05 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf06 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf07 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf08 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf09 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf10 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf11 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var asdf12 = ['a', 's', 'd', 'f']; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </script> [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedBlock.gif[/img] <script language="javascript"> [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] function ReleaseElements() [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var room = document.getElementById('container'); [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] var spans = room.all.tags('SPAN'); [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] for ( var i=0 ; i < spans.length ; ++i ) [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif[/img] [img]http://www.cnblogs.com/Images/OutliningIndicators/ContractedSubBlock.gif[/img] { [img]http://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif[/img] spans[i].Object = ''; [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif[/img] } [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </script> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </body> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img] </html> [img]http://www.cnblogs.com/Images/OutliningIndicators/None.gif[/img]

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