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authorPeter Bengtsson <mail@peterbe.com>2020-12-08 14:43:23 -0500
committerPeter Bengtsson <mail@peterbe.com>2020-12-08 14:43:23 -0500
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+---
+title: Object.preventExtensions()
+slug: Web/JavaScript/Reference/Global_Objects/Object/preventExtensions
+translation_of: Web/JavaScript/Reference/Global_Objects/Object/preventExtensions
+---
+<div>{{JSRef}}</div>
+
+<p><code><strong>Object.preventExtensions()</strong></code> 用來避免物件被新增新的屬性。</p>
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox"><code>Object.preventExtensions(<var>obj</var>)</code></pre>
+
+<h3 id="參數">參數</h3>
+
+<dl>
+ <dt><code>obj</code></dt>
+ <dd>要被用作無法擴充的物件。</dd>
+</dl>
+
+<h2 id="描述">描述</h2>
+
+<p>物件如果可以被增加新的屬性,我們稱它可以被擴充(extensible)。<code>Object.preventExtensions()</code> 標註物件使它無法被擴充,所以在它被標註為無法擴充當下,它將無法再增加新的屬性。不過注意一點,在一般狀況下,被標註為無法擴充的物件,其屬性仍可被刪除(<em>deleted</em>)。嘗試去增加屬性將會導致失敗,可能會沒有結果產生,或是傳回一個 {{jsxref("TypeError")}} (最常見,但並不是一定,當在{{jsxref("Functions_and_function_scope/Strict_mode", "strict mode", "", 1)}})。</p>
+
+<p><code>Object.preventExtensions() 只有避免物件被增加屬性,屬性仍可以被增加至 </code>object prototype 。不過,呼叫 <code>Object.preventExtensions() 使用在物件上,就可以使其 </code>{{jsxref("Object.proto", "__proto__")}} {{deprecated_inline}} 屬性無法被擴充。</p>
+
+<p>如果能把可擴充物件,轉成無法擴充物件,在 ECMAScript 5 規範中,它並沒有任何方法轉回來。</p>
+
+<h2 id="範例">範例</h2>
+
+<pre class="brush: js">// Object.preventExtensions 傳回一個被無法擴充的物件
+var obj = {};
+var obj2 = Object.preventExtensions(obj);
+obj === obj2; // true
+
+// 預設下,物件可以被擴充
+var empty = {};
+Object.isExtensible(empty); // === true
+
+// ...但是以下情況之後,無法再被變更。
+Object.preventExtensions(empty);
+Object.isExtensible(empty); // === false
+
+// Object.defineProperty throws 當為無法擴充的物件增加屬性
+var nonExtensible = { removable: true };
+Object.preventExtensions(nonExtensible);
+Object.defineProperty(nonExtensible, 'new', { value: 8675309 }); // throws a TypeError
+
+// 在 strict mode 中,嘗試去新增屬性給無法擴充物件,將 throws 出一個 TypeError。
+function fail() {
+ 'use strict';
+ nonExtensible.newProperty = 'FAIL'; // throws a TypeError
+}
+fail();
+
+// EXTENSION (only works in engines supporting __proto__
+// (which is deprecated. Use Object.getPrototypeOf instead)):
+// A non-extensible object's prototype is immutable.
+var fixed = Object.preventExtensions({});
+fixed.__proto__ = { oh: 'hai' }; // throws a TypeError
+</pre>
+
+<h2 id="筆記">筆記</h2>
+
+<p>在ES5中,如果給祝個方法的參數為非物件,它將造成一個 {{jsxref("TypeError")}} 。不過在 ES6 中,非物件參數會被正常處理。另外,如果它原本就是個無法擴充物件,就只是回傳本身。</p>
+
+<pre class="brush: js">Object.preventExtensions(1);
+// TypeError: 1 is not an object (ES5 code)
+
+Object.preventExtensions(1);
+// 1 (ES6 code)
+</pre>
+
+<h2 id="規範">規範</h2>
+
+<table class="standard-table">
+ <tbody>
+ <tr>
+ <th scope="col">Specification</th>
+ <th scope="col">Status</th>
+ <th scope="col">Comment</th>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES5.1', '#sec-15.2.3.10', 'Object.preventExtensions')}}</td>
+ <td>{{Spec2('ES5.1')}}</td>
+ <td>Initial definition. Implemented in JavaScript 1.8.5.</td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES6', '#sec-object.preventextensions', 'Object.preventExtensions')}}</td>
+ <td>{{Spec2('ES6')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ESDraft', '#sec-object.preventextensions', 'Object.preventExtensions')}}</td>
+ <td>{{Spec2('ESDraft')}}</td>
+ <td> </td>
+ </tr>
+ </tbody>
+</table>
+
+<h2 id="瀏覽器相容度">瀏覽器相容度</h2>
+
+<div>{{CompatibilityTable}}</div>
+
+<div id="compat-desktop">
+<table class="compat-table">
+ <tbody>
+ <tr>
+ <th>Feature</th>
+ <th>Chrome</th>
+ <th>Firefox (Gecko)</th>
+ <th>Internet Explorer</th>
+ <th>Opera</th>
+ <th>Safari</th>
+ </tr>
+ <tr>
+ <td>Basic support</td>
+ <td>{{CompatChrome("6")}}</td>
+ <td>{{CompatGeckoDesktop("2.0")}}</td>
+ <td>{{CompatIE("9")}}</td>
+ <td>{{CompatOpera("12")}}</td>
+ <td>{{CompatSafari("5.1")}}</td>
+ </tr>
+ <tr>
+ <td>ES6 behavior for non-object argument</td>
+ <td>{{CompatChrome("44")}}</td>
+ <td>{{CompatGeckoDesktop("35.0")}}</td>
+ <td>{{CompatIE("11")}}</td>
+ <td>{{CompatOpera("31")}}</td>
+ <td>{{CompatUnknown}}</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+ <tr>
+ <th>Feature</th>
+ <th>Android</th>
+ <th>Chrome for Android</th>
+ <th>Firefox Mobile (Gecko)</th>
+ <th>IE Mobile</th>
+ <th>Opera Mobile</th>
+ <th>Safari Mobile</th>
+ </tr>
+ <tr>
+ <td>Basic support</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ </tr>
+ <tr>
+ <td>ES6 behavior for non-object argument</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatGeckoMobile("35.0")}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ <td>{{CompatUnknown}}</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="閱讀更多">閱讀更多</h2>
+
+<ul>
+ <li>{{jsxref("Object.isExtensible()")}}</li>
+ <li>{{jsxref("Object.seal()")}}</li>
+ <li>{{jsxref("Object.isSealed()")}}</li>
+ <li>{{jsxref("Object.freeze()")}}</li>
+ <li>{{jsxref("Object.isFrozen()")}}</li>
+ <li>{{jsxref("Reflect.preventExtensions()")}}</li>
+</ul>