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146 lines
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146 lines
8.8 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<p><strong><code>handler.getOwnPropertyDescriptor()</code></strong> 方法是 <a href="Reference/Global_Objects/Object/getOwnPropertyDescriptor" title="Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符。（自有属性指的是直接赋予该对象的属性，不需要从原型链上进行查找的属性）"><code>Object.getOwnPropertyDescriptor()</code></a> 的陷阱。</p>
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<h2 id="语法">语法</h2>
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<pre><code class="language-javascript">var p = new Proxy(target, {
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getOwnPropertyDescriptor: function(target, prop) {
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}
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});
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</code></pre>
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<h3 id="参数">参数</h3>
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<p><code>下列参数会被传入 getOwnPropertyDescriptor</code> 方法中。这是绑定到处理程序。 </p>
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<dl>
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<dt><code>target</code></dt>
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<dd>目标对象。</dd>
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<dt><code>prop</code></dt>
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<dd>返回属性名称的描述。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p><code>getOwnPropertyDescriptor</code> 方法必须返回一个 object 或 u<code>ndefined。</code></p>
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<h2 id="描述">描述</h2>
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<p><code><strong>handler.getOwnPropertyDescriptor()</strong></code> 方法是 <a href="Reference/Global_Objects/Object/getOwnPropertyDescriptor" title="Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符。（自有属性指的是直接赋予该对象的属性，不需要从原型链上进行查找的属性）"><code>Object.getOwnPropertyDescriptor()</code></a> 的陷阱。</p>
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<h3 id="拦截">拦截</h3>
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<p>这个陷阱可以拦截这些操作：</p>
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<ul>
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<li><a href="Reference/Global_Objects/Object/getOwnPropertyDescriptor" title="Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符。（自有属性指的是直接赋予该对象的属性，不需要从原型链上进行查找的属性）"><code>Object.getOwnPropertyDescriptor()</code></a></li>
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<li><a href="Reference/Global_Objects/Reflect/getOwnPropertyDescriptor" title="静态方法 Reflect.getOwnPropertyDescriptor() 与 Object.getOwnPropertyDescriptor() 方法相似。如果在对象中存在，则返回给定的属性的属性描述符。否则返回 undefined。"><code>Reflect.getOwnPropertyDescriptor()</code></a></li>
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</ul>
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<h3 id="不变量">不变量</h3>
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<p>如果下列不变量被违反，代理将抛出一个 <a href="Reference/Global_Objects/TypeError" title="TypeError（类型错误） 对象用来表示值的类型非预期类型时发生的错误。"><code>TypeError</code></a>：</p>
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<ul>
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<li><code>getOwnPropertyDescriptor</code> 必须返回一个 object 或 u<code>ndefined。</code></li>
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<li>如果属性作为目标对象的不可配置的属性存在，则该属性无法报告为不存在。</li>
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<li>如果属性作为目标对象的属性存在，并且目标对象不可扩展，则该属性无法报告为不存在。</li>
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<li>如果属性不存在作为目标对象的属性，并且目标对象不可扩展，则不能将其报告为存在。</li>
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<li>属性不能被报告为不可配置，如果它不作为目标对象的自身属性存在，或者作为目标对象的可配置的属性存在。</li>
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<li>Object.getOwnPropertyDescriptor（target）的结果可以使用 Object.defineProperty 应用于目标对象，也不会抛出异常。</li>
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</ul>
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<h2 id="示例">示例</h2>
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<p>以下是 <a href="Reference/Global_Objects/Object/getOwnPropertyDescriptor" title="Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符。（自有属性指的是直接赋予该对象的属性，不需要从原型链上进行查找的属性）"><code>Object.getOwnPropertyDescriptor()</code></a> 的代码陷阱：</p>
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<pre><code class="language-javascript">var p = new Proxy({ a: 20}, {
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getOwnPropertyDescriptor: function(target, prop) {
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console.log('called: ' + prop);
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return { configurable: true, enumerable: true, value: 10 };
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}
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});
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console.log(Object.getOwnPropertyDescriptor(p, 'a').value); // "called: a"
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// 10
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</code></pre>
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<p>以下代码则违反了不变量。</p>
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<pre><code class="language-javascript">var obj = { a: 10 };
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Object.preventExtensions(obj);
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var p = new Proxy(obj, {
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getOwnPropertyDescriptor: function(target, prop) {
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return undefined;
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}
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});
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Object.getOwnPropertyDescriptor(p, 'a'); // TypeError is thrown
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</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/ecma-262/6.0/#sec-proxy-object-internal-methods-and-internal-slots-getownproperty-p" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">[[GetOwnProperty]]</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>Initial definition.</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-proxy-object-internal-methods-and-internal-slots-getownproperty-p" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">[[GetOwnProperty]]</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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<div><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></div>
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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: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><a href="/en-US/Firefox/Releases/18" title="Released on 2013-01-08.">18</a> (18)</td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</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: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td>18.0 (18)</td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
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<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</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="相关链接">相关链接</h2>
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<ul>
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<li><a href="Reference/Global_Objects/Proxy" title="Proxy 对象用于定义基本操作的自定义行为（如属性查找，赋值，枚举，函数调用等）。"><code>Proxy</code></a></li>
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<li><a href="Reference/Global_Objects/Proxy/handler" title="处理器对象用来自定义代理对象的各种可代理操作。"><code>handler</code></a></li>
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<li><a href="Reference/Global_Objects/Object/getOwnPropertyDescriptor" title="Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符。（自有属性指的是直接赋予该对象的属性，不需要从原型链上进行查找的属性）"><code>Object.getOwnPropertyDescriptor()</code></a></li>
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<li><a href="Reference/Global_Objects/Reflect/getOwnPropertyDescriptor" title="静态方法 Reflect.getOwnPropertyDescriptor() 与 Object.getOwnPropertyDescriptor() 方法相似。如果在对象中存在，则返回给定的属性的属性描述符。否则返回 undefined。"><code>Reflect.getOwnPropertyDescriptor()</code></a></li>
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</ul>
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</article> |