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162 lines
10 KiB
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<article id="wikiArticle">
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<div></div>
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<p><code><strong>hasOwnProperty()</strong></code> 方法会返回一个布尔值，指示对象<strong>自身</strong>属性中是否具有指定的属性</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code><em>obj</em>.hasOwnProperty(<em>prop</em>)</code></code></pre>
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<h3 id="Parameters" name="Parameters">参数</h3>
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<dl>
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<dt><code>prop</code></dt>
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<dd>要检测的属性 <a href="Reference/String" title="此页面仍未被本地化, 期待您的翻译!"><code>字符串</code></a> 名称或者 <a href="Reference/Global_Objects/Symbol" title='Symbol()函数会返回symbol类型的值，该类型具有静态属性和静态方法。它的静态属性会暴露几个内建的成员对象；它的静态方法会暴露全局的symbol注册，且类似于内建对象类，但作为构造函数来说它并不完整，因为它不支持语法："new Symbol()"。'><code>Symbol</code></a>。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p>用来判断某个对象是否含有指定的属性的 <a href="Reference/Boolean" title="此页面仍未被本地化, 期待您的翻译!"><code>Boolean</code></a> 。</p>
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<h2 id="Description" name="Description">描述</h2>
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<p>所有继承了 <a href="Reference/Global_Objects/Object" title="Object 构造函数创建一个对象包装器。"><code>Object</code></a> 的对象都会继承到 <code>hasOwnProperty</code> 方法。这个方法可以用来检测一个对象是否含有特定的自身属性；和 <a href="Reference/Operators/in" title="如果指定的属性在指定的对象或其原型链中，则in 运算符返回true。"><code>in</code></a> 运算符不同，该方法会忽略掉那些从原型链上继承到的属性。</p>
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<h2 id="Examples" name="Examples">示例</h2>
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<h3 id="Example:_Using_hasOwnProperty_to_test_for_a_property.27s_existence" name="Example:_Using_hasOwnProperty_to_test_for_a_property.27s_existence">使用 <code>hasOwnProperty</code> 方法判断属性是否存在</h3>
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<p>下面的例子检测了对象 <code>o</code> 是否含有自身属性 <code>prop：</code></p>
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<pre><code class="language-javascript">o = new Object();
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o.prop = 'exists';
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function changeO() {
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o.newprop = o.prop;
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delete o.prop;
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}
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o.hasOwnProperty('prop'); // 返回 true
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changeO();
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o.hasOwnProperty('prop'); // 返回 false</code></pre>
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<h3 id="Example:_Direct_versus_inherited_properties" name="Example:_Direct_versus_inherited_properties">自身属性与继承属性</h3>
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<p>下面的例子演示了 <code>hasOwnProperty</code> 方法对待自身属性和继承属性的区别：</p>
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<pre><code class="language-javascript">o = new Object();
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o.prop = 'exists';
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o.hasOwnProperty('prop'); // 返回 true
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o.hasOwnProperty('toString'); // 返回 false
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o.hasOwnProperty('hasOwnProperty'); // 返回 false</code></pre>
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<h3 id="Example:_Itarate_over_properties_not_considering_inherited_properties" name="Example:_Itarate_over_properties_not_considering_inherited_properties">遍历一个对象的所有自身属性</h3>
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<p>下面的例子演示了如何在遍历一个对象的所有属性时忽略掉继承属性，注意这里 <a href="Reference/Statements/for...in" title="for...in语句以任意顺序遍历一个对象的可枚举属性。对于每个不同的属性，语句都会被执行。"><code>for...in</code></a> 循环只会遍历可枚举属性，所以不应该基于这个循环中没有不可枚举的属性而得出 <code>hasOwnProperty 是严格限制于可枚举项目的（如同 </code><a href="Reference/Global_Objects/Object/getOwnPropertyNames" title="Object.getOwnPropertyNames()方法返回一个由指定对象的所有自身属性的属性名（包括不可枚举属性但不包括Symbol值作为名称的属性）组成的数组。"><code>Object.getOwnPropertyNames()</code></a>）。</p>
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<pre><code class="language-javascript">var buz = {
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fog: 'stack'
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};
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for (var name in buz) {
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if (buz.hasOwnProperty(name)) {
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alert("this is fog (" + name + ") for sure. Value: " + buz[name]);
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}
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else {
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alert(name); // toString or something else
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}
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}</code></pre>
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<h3 id="使用_hasOwnProperty_作为属性名"><code>使用 hasOwnProperty</code> 作为属性名</h3>
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<p>JavaScript 并没有保护 hasOwnProperty 属性名，因此某个对象是有可能存在使用这个属性名的属性，使用<strong>外部</strong>的 <code>hasOwnProperty 获得正确的结果是需要的：</code></p>
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<pre><code class="language-javascript">var foo = {
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hasOwnProperty: function() {
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return false;
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},
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bar: 'Here be dragons'
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};
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foo.hasOwnProperty('bar'); // 始终返回 false
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// 如果担心这种情况，可以直接使用原型链上真正的 hasOwnProperty 方法
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({}).hasOwnProperty.call(foo, 'bar'); // true
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// 也可以使用 Object 原型上的 hasOwnProperty 属性
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Object.prototype.hasOwnProperty.call(foo, 'bar'); // true</code></pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</th>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf" hreflang="en" lang="en" rel="noopener" title="ECMAScript 3rd Edition (ECMA-262)">ECMAScript 3rd Edition (ECMA-262)</a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>Initial definition. Implemented in JavaScript 1.5.</td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.5" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Object.prototype.hasOwnProperty</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-object.prototype.hasownproperty" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Object.prototype.hasOwnProperty</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://tc39.github.io/ecma262/#sec-object.prototype.hasownproperty" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Object.prototype.hasOwnProperty</small></a></td>
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<td><span class="spec-Draft">Draft</span></td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
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<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
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This compatibility table still uses the old format,
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because we haven't yet converted the data it contains.
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<strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
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<div class="htab">
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<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
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<ul>
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<li class="selected"><a>Desktop</a></li>
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<li><a>Mobile</a></li>
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</ul>
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</div><p></p>
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<div id="compat-desktop">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Chrome</th>
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<th>Firefox (Gecko)</th>
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<th>Internet Explorer</th>
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<th>Opera</th>
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<th>Safari</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<div id="compat-mobile">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Android</th>
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<th>Chrome for Android</th>
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<th>Firefox Mobile (Gecko)</th>
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<th>IE Mobile</th>
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<th>Opera Mobile</th>
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<th>Safari Mobile</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<h2 id="See_Also" name="See_Also">相关链接</h2>
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<ul>
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<li><a href="/zh-CN/docs/Enumerability_and_ownership_of_properties" title="/zh-CN/docs/Enumerability_and_ownership_of_properties">属性的可枚举性和所有权</a></li>
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<li><a href="Reference/Global_Objects/Object/getOwnPropertyNames" title="Object.getOwnPropertyNames()方法返回一个由指定对象的所有自身属性的属性名（包括不可枚举属性但不包括Symbol值作为名称的属性）组成的数组。"><code>Object.getOwnPropertyNames()</code></a></li>
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<li><a href="Reference/Statements/for...in" title="for...in语句以任意顺序遍历一个对象的可枚举属性。对于每个不同的属性，语句都会被执行。"><code>for...in</code></a></li>
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<li><a href="Reference/Operators/in" title="如果指定的属性在指定的对象或其原型链中，则in 运算符返回true。"><code>in</code></a></li>
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<li><a href="Guide/Inheritance_Revisited">JavaScript 教程: 再谈继承</a></li>
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</ul>
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</article> |