JavaScript初学者应注意的七个细节

（1）简化代码

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JavaScript定义对象和数组非常简单，我们想要创建一个对象，一般是这样写的：<wbr><wbr></wbr></wbr>

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var car = new Object(); car.colour = 'red' ; car.wheels = 4; car.hubcaps = 'spinning' ; car.age = 4;

下面的写法可以达到同样的效果：

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var car = { <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> colour: 'red' , <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> wheels:4, 　　hubcaps: 'spinning' , 　　age:4 }

后面的写法要短得多，而且你不需要重复写对象名称。

另外对于数组同样有简洁的写法，过去我们声明数组是这样写的：

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var moviesThatNeedBetterWrit<wbr>ers =</wbr> new Array( <wbr><wbr></wbr></wbr> 'Transformers' , 'Transformers2' , 'Avatar' , 'Indiana Jones 4' );

更简洁的写法是：<wbr></wbr>

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var moviesThatNeedBetterWrit<wbr>ers = [</wbr> <wbr><wbr></wbr></wbr> 'Transformers' , 'Transformers2' , 'Avatar' , 'Indiana Jones 4' ];

对于数组，还有关联数组这样一个特别的东西。<wbr>你会发现很多代码是这样定义对象的：</wbr>

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var car = new Array(); car[ 'colour' ] = 'red' ; car[ 'wheels' ] = 4; car[ 'hubcaps' ] = 'spinning' ; car[ 'age' ] = 4;

这太疯狂了，不要觉得困惑，“关联数组”只是对象的一个别名而已。

另外一个简化代码的方法是使用三元运算符，举个例子：

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var direction; if (x < 200){ <wbr><wbr></wbr></wbr> direction = 1; } else { <wbr><wbr></wbr></wbr> direction = -1; }

我们可以使用如下的代码替换这种写法：

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1	var direction = x < 200 ? 1 : -1;

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（2）使用JSON作为数据格式 <wbr><wbr></wbr></wbr>

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伟大的Douglas Crockford发明了JSON数据格式来存储数据，你可以使用原生的javascript方法来存储复杂的数据而不需要进行任何额外的转换，例如：

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var band = { <wbr><wbr></wbr></wbr> "name" : "The Red Hot Chili Peppers" , <wbr><wbr></wbr></wbr> "members" :[ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> { <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "name" : "Anthony Kiedis" , <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "role" : "lead vocals" <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> }, <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> { <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "name" : "Michael 'Flea' Balzary" , <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "role" : "bass guitar, trumpet, backing vocals" <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> }, <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> { <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "name" : "Chad Smith" , <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "role" : "drums,percussion" <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> }, <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> { <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "name" : "John Frusciante" , <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> "role" : "Lead Guitar" <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> } <wbr><wbr></wbr></wbr> ], <wbr><wbr></wbr></wbr> "year" : "2009" }

你可以使用在JavaScript中直接使用JSON，甚至作为API返回的一种格式，在许多的API中被应用，例如：

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< div id = "delicious" ></ div >< script > function delicious(o){ <wbr><wbr></wbr></wbr> var out = '< ul >'; <wbr><wbr></wbr></wbr> for(var i=0;i< o.length ;i++){ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> out += '<li>< a href = "' + o[i].u + '" >' + <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> o[i].d + '</ a ></ li >'; <wbr><wbr></wbr></wbr> } <wbr><wbr></wbr></wbr> out += '</ ul >'; <wbr><wbr></wbr></wbr> document.getElementByIdx_x('delicious').innerHTML = out; } </ script > < script src = "http://feeds.delicious.com/v2/json/codepo8/javascript?count=15&callback=delicious" ></ script >

这里调用delicious 的Web服务获取最新书签，以JSON格式返回，然后将它们显示成无序列表的形式。

从本质上讲，JSON是用于描述复杂的数据最轻量级的方式，而且直接它运行在浏览器中。<wbr>你甚至可以在PHP中调用 json_decode（）函数来使用它。</wbr>

（3）尽量使用JavaScript原生函数<wbr></wbr>

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要找一组数字中的最大数，我们可能会写一个循环，例如：

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var numbers = [3,342,23,22,124]; var max = 0; for ( var i=0;i<numbers.length;i++){ <wbr><wbr></wbr></wbr> if (numbers[i] > max){ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> max = numbers[i]; <wbr><wbr></wbr></wbr> } } alert(max);

其实，不用循环可以实现同样的功能：

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var numbers = [3,342,23,22,124]; numbers.sort( function (a,b){ return b - a}); alert(numbers[0]);

而最简洁的写法是：

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1	Math.max(12,123,3,2,433,4); // returns 433

你甚至可以使用Math.max来检测浏览器支持哪个属性：

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var scrollTop= Math.max( <wbr></wbr> doc.documentElement.scrollTop, <wbr></wbr> doc.body.scrollTop );

如果你想给一个元素增加class样式，可能原始的写法是这样的：

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function addclass(elm,newclass){ <wbr><wbr></wbr></wbr> var c = elm.className; <wbr><wbr></wbr></wbr> elm.className = (c === '' ) ? newclass : c+ ' ' +newclass;

而更优雅的写法是：

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function addclass(elm,newclass){ <wbr><wbr></wbr></wbr> var classes = elm.className.split( ' ' ); <wbr><wbr></wbr></wbr> classes.push(newclass); <wbr><wbr></wbr></wbr> elm.className = classes.join( ' ' ); }

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（4）事件委托

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事件是JavaScript非常重要的一部分。我们想给一个列表中的链接绑定点击事件，一般的做法是写一个循环，给每个链接对象绑定事件，HTML代码如下：

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<h2>Great Web resources</h2> <ul id= "resources" > <wbr><wbr></wbr></wbr> <li><a href= "http://opera.com/wsc" >Opera Web Standards Curriculum</a></li> <wbr><wbr></wbr></wbr> <li><a href= "http://sitepoint.com" >Sitepoint</a></li> <wbr><wbr></wbr></wbr> <li><a href= "http://alistapart.com" >A List Apart</a></li> <wbr><wbr></wbr></wbr> <li><a href= "http://yuiblog.com" >YUI Blog</a></li> <wbr><wbr></wbr></wbr> <li><a href= "http://blameitonthevoices.com" >Blame it on the voices</a></li> <wbr><wbr></wbr></wbr> <li><a href= "http://oddlyspecific.com" >Oddly specific</a></li> </ul>

脚本如下：

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// Classic event handling example ( function (){ <wbr><wbr></wbr></wbr> var resources = document.getElementByIdx_x( 'resources' ); <wbr><wbr></wbr></wbr> var links = resources.getElementsByTagName_r( 'a' ); <wbr><wbr></wbr></wbr> var all = links.length; <wbr><wbr></wbr></wbr> for ( var i=0;i<all;i++){ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> // Attach a listener to each link <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> links[i].addEventListener( 'click' ,handler, false ); <wbr><wbr></wbr></wbr> }; <wbr><wbr></wbr></wbr> function handler(e){ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> var x = e.target; // Get the link that was clicked <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> alert(x); <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> e.preventDefault(); <wbr><wbr></wbr></wbr> }; })();

更合理的写法是只给列表的父对象绑定事件，代码如下：

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( function (){ <wbr><wbr></wbr></wbr> var resources = document.getElementByIdx_x( 'resources' ); <wbr><wbr></wbr></wbr> resources.addEventListener( 'click' ,handler, false ); <wbr><wbr></wbr></wbr> function handler(e){ <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> var x = e.target; // get the link tha <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> if (x.nodeName.toLowerCase() === 'a' ){ <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> alert( 'Event delegation:' + x); <wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> e.preventDefault(); <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr> } <wbr><wbr></wbr></wbr> }; })();

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（5）匿名函数

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关于JavaScript的最头疼的事情之一是，它的变量没有特定的作用范围。<wbr>一般情况下，任何变量，函数，数组或对象都是全局性，这意味着在同一页上的其他脚本可以访问并覆盖它们。解决方法是把变量封装在一个匿名函数中。<wbr>例如，下面的定义将产生三个全局变量和和两个全局函数： <div> <div> <div javascript=""> <div><a href="http://www.cnblogs.com/lhb25/archive/2011/01/10/1932284.html#">?</a></div> <table cellspacing="0" cellpadding="0" border="0"><tbody><tr> <td> <div index0="" number1="">1</div> <div index1="" number2="">2</div> <div index2="" number3="">3</div> <div index3="" number4="">4</div> <div index4="" number5="">5</div> <div index5="" number6="">6</div> <div index6="" number7="">7</div> <div index7="" number8="">8</div> <div index8="" number9="">9</div> </td> <td> <div> <div index0="" number1=""> <code>var</code> <code>name =</code> <code>'Chris'</code><code>;</code> </div> <div index1="" number2=""> <code>var</code> <code>age =</code> <code>'34'</code><code>;</code> </div> <div index2="" number3=""> <code>var</code> <code>status =</code> <code>'single'</code><code>;</code> </div> <div index3="" number4=""> <code>function</code> <code>createMember(){</code> </div> <div index4="" number5=""> <code><wbr><wbr></wbr></wbr></code><code>// [...]</code> </div> <div index5="" number6=""><code>}</code></div> <div index6="" number7=""> <code>function</code> <code>getMemberDetails(){</code> </div> <div index7="" number8=""> <code><wbr><wbr></wbr></wbr></code><code>// [...]</code> </div> <div index8="" number9=""><code>}</code></div> </div> </td> </tr></tbody></table> </div> </div> </div> <p>封装后如下：</p> <div> <div> <div javascript=""> <div><a href="http://www.cnblogs.com/lhb25/archive/2011/01/10/1932284.html#">?</a></div> <table cellspacing="0" cellpadding="0" border="0"><tbody><tr> <td> <div index0="" number1="">1</div> <div index1="" number2="">2</div> <div index2="" number3="">3</div> <div index3="" number4="">4</div> <div index4="" number5="">5</div> <div index5="" number6="">6</div> <div index6="" number7="">7</div> <div index7="" number8="">8</div> <div index8="" number9="">9</div> <div index9="" number10="">10</div> <div index10="" number11="">11</div> <div index11="" number12="">12</div> <div index12="" number13="">13</div> <div index13="" number14="">14</div> <div index14="" number15="">15</div> </td> <td> <div> <div index0="" number1=""> <code>var</code> <code>myApplication =</code> <code>function</code><code>(){</code> </div> <div index1="" number2=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>name =</code> <code>'Chris'</code><code>;</code> </div> <div index2="" number3=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>age =</code> <code>'34'</code><code>;</code> </div> <div index3="" number4=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>status =</code> <code>'single'</code><code>;</code> </div> <div index4="" number5=""> <code><wbr><wbr></wbr></wbr></code><code>return</code><code>{</code> </div> <div index5="" number6=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>createMember:</code><code>function</code><code>(){</code> </div> <div index6="" number7=""> <code><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></code><code>// [...]</code> </div> <div index7="" number8=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>},</code> </div> <div index8="" number9=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>getMemberDetails:</code><code>function</code><code>(){</code> </div> <div index9="" number10=""> <code><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></code><code>// [...]</code> </div> <div index10="" number11=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>}</code> </div> <div index11="" number12=""> <code><wbr><wbr></wbr></wbr></code><code>}</code> </div> <div index12="" number13=""><code>}();</code></div> <div index13="" number14=""><code>// myApplication.createMember() and</code></div> <div index14="" number15=""><code>// myApplication.getMemberDetails() now works.</code></div> </div> </td> </tr></tbody></table> </div> </div> </div> <p>这被称为单体模式，是JavaScript设计模式的一种，这种模式在YUI中用得非常多，改进的写法是： <wbr></wbr></p> <div> <div> <div javascript=""> <div><a href="http://www.cnblogs.com/lhb25/archive/2011/01/10/1932284.html#">?</a></div> <table cellspacing="0" cellpadding="0" border="0"><tbody><tr> <td> <div index0="" number1="">1</div> <div index1="" number2="">2</div> <div index2="" number3="">3</div> <div index3="" number4="">4</div> <div index4="" number5="">5</div> <div index5="" number6="">6</div> <div index6="" number7="">7</div> <div index7="" number8="">8</div> <div index8="" number9="">9</div> <div index9="" number10="">10</div> <div index10="" number11="">11</div> <div index11="" number12="">12</div> <div index12="" number13="">13</div> <div index13="" number14="">14</div> <div index14="" number15="">15</div> <div index15="" number16="">16</div> </td> <td> <div> <div index0="" number1=""> <code>var</code> <code>myApplication =</code> <code>function</code><code>(){</code> </div> <div index1="" number2=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>name =</code> <code>'Chris'</code><code>;</code> </div> <div index2="" number3=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>age =</code> <code>'34'</code><code>;</code> </div> <div index3="" number4=""> <code><wbr><wbr></wbr></wbr></code><code>var</code> <code>status =</code> <code>'single'</code><code>;</code> </div> <div index4="" number5=""> <code><wbr><wbr></wbr></wbr></code><code>function</code> <code>createMember(){</code> </div> <div index5="" number6=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>// [...]</code> </div> <div index6="" number7=""> <code><wbr><wbr></wbr></wbr></code><code>}</code> </div> <div index7="" number8=""> <code><wbr><wbr></wbr></wbr></code><code>function</code> <code>getMemberDetails(){</code> </div> <div index8="" number9=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>// [...]</code> </div> <div index9="" number10=""> <code><wbr><wbr></wbr></wbr></code><code>}</code> </div> <div index10="" number11=""> <code><wbr><wbr></wbr></wbr></code><code>return</code><code>{</code> </div> <div index11="" number12=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>create:createMember,</code> </div> <div index12="" number13=""> <code><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></code><code>get:getMemberDetails</code> </div> <div index13="" number14=""> <code><wbr><wbr></wbr></wbr></code><code>}</code> </div> <div index14="" number15=""><code>}();</code></div> <div index15="" number16=""><code>//myApplication.get() and myApplication.create() now work.</code></div> </div> </td> </tr></tbody></table> </div> </div> </div> <p><wbr><wbr></wbr></wbr></p> <p><strong>（</strong>6<strong>）代码可配置</strong></p> <hr> <p> 你写的代码如果想让别人更容易进行使用或者修改，则需要可配置，解决方案是在你写的脚本中增加一个配置对象。要点如下：<wbr><br><wbr><br> 1、在你的脚本中新增一个叫configuration的对象。</wbr></wbr></p> <p>2、在配置对象中存放所有其它人可能想要去改变的东西，例如CSS的ID、class名称、语言等等。</p> <p>3、返回这个对象，作为公共属性以便其它人可以进行重写。<wbr></wbr></p> <wbr><p><wbr></wbr></p> <p><strong>（</strong>7<strong>）代码兼容性</strong></p> <hr> <p> 　　兼容性是初学者容易忽略的部分，通常学习Javascript的时候都是在某个固定的浏览器中进行测试，而这个浏览器很有可能就是IE，这是非常致命的，因为目前几大主流浏览器中偏偏IE对标准的支持是最差的。最终用户看到的结果也许就是，你写的代码在某个浏览器无法正确运行。你应该把你的代码在主流的浏览器中都测试一下，这也许很费时间，但是应该这样做。<wbr><wbr></wbr></wbr></p> </wbr></wbr></wbr>