JavaScript面向对象精要(一)

数据类型

在JavaScript中，数据类型分为两类：

• 原始类型：保存一些简单数据，如true，5等。JavaScript共有5中原始类型： 
  
  • boolean：布尔，值为true或false
  • number：数字，值为任何整型会浮点数值
  • string：字符串，值为由单引号或双引号括出的单个字符或连续字符（JavaScript不区分字符类型）
  • null：空类型，其仅有一个值：nulll
  • undefined：未定义，其仅有一个值：undefined

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> blog = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.ido321.com"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> age = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>;alert(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typeof</span> blog); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"string"</span>alert(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typeof</span> age); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"number"</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

原始类型的值是直接保存在变量中，并可以用typeof进行检测。但是typeof对null的检测是返回object,而不是返回null：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//弹出Not null</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typeof</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>){    alert(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Not null"</span>);   }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>{    alert(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"null"</span>);}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

所以检测null时，最好用全等于(===),其还能避免强制类型转换：

<code class="hljs coffeescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"21"</span> === <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>);  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"21"</span> == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>);  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">undefined</span> == <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>);  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">undefined</span> === <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>);  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

对于字符串、数字或者布尔值，其都有对应的方法，这些方法来自于对应的原始封装类型：String、Number和Boolean。原始封装类型将被自动创建。

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> = name.charAt(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);console.log(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"P"</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

在JavaScript引擎中发生的事情：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> temp = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String(name);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> = temp.charAt(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);temp = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;console.log(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"P"</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

字符串对象的引用在用完之后立即被销毁，所以不能给字符串添加属性，并且instanceof检测对应类型时均返回false：

<code class="hljs coffeescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-reserved" style="box-sizing: border-box;">var</span> name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>;name.age = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>;<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(name.age);   <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">undefined</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(name <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">instanceof</span> String);  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span><span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

• 引用类型：保存为对象，实质是指向内存位置的引用，所以不在变量中保存对象。除了自定义的对象，JavaScript提供了6中内建类型： 
  
  • Array：数组类型，以数字为索引的一组值的有序列表
  • Date：日期和时间类型
  • Error：运行期错误类型
  • Function：函数类型
  • Object：通用对象类型
  • RegExp：正则表达式类型 
    可以用new来实例化每一个对象，或者用字面量形式来创建对象：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> obj = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> own = {            name:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>,            blog:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.ido321.com"</span>,            <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"my age"</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>        };console.log(own.blog);    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//访问属性</span>console.log(own[<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"my age"</span>]); obj = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">null</span>;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//解除引用</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

obj 并不包含对象实例，而是一个指向内存中实际对象所在位置的指针（或者说引用）。因为typeof对所有非函数的引用类型均返回object，所以需要用instanceof来检测引用类型。

函数

在JavaScript中，函数就是对象。使函数不同于其他对象的决定性特性是函数存在一个被称为[[Call]]的内部属性。内部属性无法通过代码访问而是定义了代码执行时的行为。

创建形式

1、函数声明：用function关键字，会被提升至上下文 
2、函数表达式：不能被提升 
3、实例化Function内建类型

<code class="hljs coffeescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">sayHi();    <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span>函数提升<span class="hljs-reserved" style="box-sizing: border-box;">function</span> sayHi(){    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello"</span>);}<span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span>其他等效等效方式/*<span class="hljs-reserved" style="box-sizing: border-box;">var</span> sayHi = <span class="hljs-reserved" style="box-sizing: border-box;">function</span>(){     <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">console</span>.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello"</span>);}<span class="hljs-reserved" style="box-sizing: border-box;">var</span> sayHi = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Function(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" console.log(\"Hello\");"</span>);*/</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

参数

JavaScript函数的另外一个独特之处在于可以给函数传递任意数量的参数。函数参数被保存在arguments类数组对象中，其自动存在函数中，能通过数字索引来引用参数，但它不是数组实例：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">alert(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Array</span>.isArray(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">arguments</span>));   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

类数组对象arguments 保存的是函数的实参，但并不会忽略形参。因而，arguments.length返回实参列表的长度，arguments.callee.length返回形参列表的长度。

<code class="hljs rust has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">function <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">ref</span>(value){    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> value;}console.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">log</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">ref</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi"</span>));console.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">log</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">ref</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi"</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>));console.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">log</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">ref</span>.length);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

函数中的this

关于this的问题，可参考此文：JavaScript中的this。 
JavaScript提供了三个方法用于改变this的指向：call、apply和bind。三个函数的第一个参数都是指定this的值，其他参数均作为参数传递给函数。

对象

对象是一种引用类型，创建对象常见的两种方式：Object构造函数和对象字面量形式：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> per1 = {    name:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>,    blog:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.ido321.com"</span>};<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> per2 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>;per2.name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"不写代码的码农"</span>;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

属性操作

在JavaScript中，可以随时为对象添加属性：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">per1.age = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;per1.sayName = <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>    alert(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name);   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"Pomy"</span>}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

因而，在检测对象属性是否存在时，常犯的一个错误是：

<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//结果是<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(per1.age){    alert(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>)}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>{    alert(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>);}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

per1.age 是存在的，但是其值是0，所以不能满足if条件。if判断中的值是一个对象、非空字符串、非零数字或true时，判断会评估为真；而当值是一个null、undefined、0、false、NaN或空字符串时评估为假。 
因而，检测属性是否存在时，有另外的两种方式：in和hasOwnProperty()，前者会检测原型属性和自有(实例)属性，后者只检测自有(实例)属性。

<code class="hljs livecodeserver has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"age"</span> <span class="hljs-operator" style="box-sizing: border-box;">in</span> per1); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //true</span>console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(per1.hasOwnProperty(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"age"</span>)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //true</span>console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"toString"</span> <span class="hljs-operator" style="box-sizing: border-box;">in</span> per1); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //true</span>console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(per1.hasOwnProperty(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"toString"</span>)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

对象per1并没有定义toString，该属性继承于Object.prototype，所以in和hasOwnProperty()检测该属性时出现差异。如果只想判断一个对象属性是不是原型，可以利用如下方法：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span> <span class="hljs-title" style="box-sizing: border-box;">isPrototypeProperty</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(obj,name)</span>{</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> name <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> obj && !obj.hasOwnProperty(name);}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

若要删除一个属性，用delete操作符，用于删除自有属性，不能删除原型属性。

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span> = function(){    console<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.log</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"per1对象"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>console<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.log</span>(per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.hasOwnProperty</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"toString"</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;   //true</span>per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;   //"per1对象"</span>delete per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>console<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.log</span>(per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.hasOwnProperty</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"toString"</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;   //false</span>console<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.log</span>(per1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  //[object Object]</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

有时需要枚举对象的可枚举属性，也有两种方式：for-in循环和Object.keys()，前者依旧会遍历出原型属性，后者只返回自有属性。所有可枚举属性的内部属性[[Enumerable]]的值均为true。

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> per3 = {    name:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>,    blog:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.ido321.com"</span>,    age:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>,    getAge:<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.age;    }};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

实际上，大部分原生属性的[[Enumerable]]的值均为false，即该属性不能枚举。可以通过propertyIsEnumerable()检测属性是否可以枚举：

<code class="hljs livecodeserver has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(per3.propertyIsEnumerable(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //true</span>var pros = Object.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">keys</span>(per3); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //返回可枚举属性的名字数组</span>console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"length"</span> <span class="hljs-operator" style="box-sizing: border-box;">in</span> pros); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //true</span>console.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">log</span>(pros.propertyIsEnumerable(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"length"</span>)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"> //false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

属性name是自定义的，可枚举；属性length是Array.prototype的内建属性，不可枚举。

属性类型

属性有两种类型：数据属性和访问器属性。二者均具有四个属性特征：

• 数据属性：[[Enumerable]]、[[Configurable]]、[[Value]]和[[Writable]]
• 访问器属性：[[Enumerable]]、[[Configurable]]、[[Get]]和[[Set]]

[[Enumerable]] :布尔值，属性是否可枚举，自定义属性默认是true。 
[[Configurable]] :布尔值，属性是否可配置(可修改或可删除)，自定义属性默认是true。它是不可逆的，即设置成false后，再设置成true会报错。 
[[Value]]：保存属性的值。 
[[Writable]]：布尔值，属性是否可写，所有属性默认可写。 
[[Get]]：获取属性值。 
[[Set]]：设置属性值。 
ES 5提供了两个方法用于设置这些内部属性： 
Object.defineProperty(obj,pro,desc_map) 和 Object.defineProperties(obj,pro_map)。利用这两个方法为per3添加一个属性和创建一个新对象per4:

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.defineProperty(per3,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sex"</span>,{    value:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"male"</span>,    enumerable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>,    configurable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>, <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//属性不能删除和修改，该值也不能被设置成true</span>});console.log(per3.sex);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//'male'</span>console.log(per3.propertyIsEnumerable(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sex"</span>));  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">delete</span> per3.sex;    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//不能删除</span>per3.sex = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"female"</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//不能修改</span>console.log(per3.sex);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//'male'</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.defineProperty(per3,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sex"</span>,{    configurable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>, <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//报错</span>});per4 = {};<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.defineProperties(per4,{    name:{        value:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dwqs"</span>,        writable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>    },    blog:{        value:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://blog.92fenxiang.com"</span>    },    Name:{        get:<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name;        },        set:<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(value)</span>{</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name = value;        },        enumerable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>,        configurable:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>    }});console.log(per4.name); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//dwqs</span>per4.Name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>;console.log(per4.Name); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Pomy</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul>

需要注意的是，通过这两种方式来定义新属性时，如果不指定特征值，则默认是false,也不能创建同时具有数据特征和访问器特征的属性。可以通过Object.getOwnPropertyDescriptor()方法来获取属性特征的描述，接受两个参数：对象和属性名。若属性存在，则返回属性描述对象。

<code class="hljs axapta has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">var <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">desc</span> = Object.getOwnPropertyDescriptor(per4,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>);console.log(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">desc</span>.enumerable); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span>console.log(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">desc</span>.configurable); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span>console.log(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">desc</span>.writable); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//true</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

根据属性的属性类型，返回的属性描述对象包含其对应的四个属性特征。

禁止修改对象

对象和属性一样具有指导其行为的内部特征。其中，[[Extensible]]是一个布尔值，指明改对象本身是否可以被修改（[[Extensible]]值为true）。创建的对象默认都是可以扩展的，可以随时添加新的属性。 
ES5提供了三种方式：

• Object.preventExtensions(obj)：创建不可扩展的obj对象，可以利用Object.isExtensible(obj)来检测obj是否可以扩展。严格模式下给不扩展对象添加属性会报错，非严格模式下则添加失败。
• Object.seal(obj)：封印对象，此时obj的属性变成只读，不能添加、改变或删除属性（所有属性都不可配置），其[[Extensible]]值为false,[[Configurable]]值为false。可以利用Object.isSealed(obj)来检测obj是否被封印。
• Object.freeze(obj)：冻结对象，不能在冻结对象上添加或删除属性，不能改变属性类型，也不能写入任何数据类型。可以利用Object.isFrozen(obj)来检测obj是否被冻结。

注意：冻结对象和封印对象均要在严格模式下使用。

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-pi" style="color: rgb(0, 102, 102); box-sizing: border-box;">"use strict"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> per5 = {    name:<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>};console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isExtensible(per5));   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//true</span>console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isSealed(per5));         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span>console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isFrozen(per5));       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.freeze(per5);console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isExtensible(per5));   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span>console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isSealed(per5));       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//true</span>console.log(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.isFrozen(per5));       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//true</span>per5.name=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dwqs"</span>;console.log(per5.name);   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"Pomy"</span>per5.Hi = <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>    console.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi"</span>);};console.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi"</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> per5);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">delete</span> per5.name;console.log(per5.name);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"Pomy"</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> desc = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.getOwnPropertyDescriptor(per5,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>);console.log(desc.configurable);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span>console.log(desc.writable);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//false</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>

注意，禁止修改对象的三个方法只对对象的自有属性有效，对原型对象的属性无效，仍然可以在原型上添加或修改属性。

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span> <span class="hljs-title" style="box-sizing: border-box;">Person</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(name)</span>{</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name = name;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> person1 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Person(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pomy"</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> person2 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Person(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dwqs"</span>);<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>.freeze(person1);Person.prototype.Hi = <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>    console.log(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi"</span>);};person1.Hi();  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"Hi";</span>person2.Hi();  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//"Hi";</span></code>