uTools-Manuals/docs/javascript/Reference/Global_Objects/Proxy/handler/isExtensible.html

<article id="wikiArticle">
<div>handler.isExtensible()用于拦截对对象的Object.isExtensible()。</div>
<h2 id="语法">语法</h2>
<pre><code  class="language-javascript">var p = new Proxy(target, {
  isExtensible: function(target) {
  }
});
</code></pre>
<h3 id="参数">参数</h3>
<p>下列参数将会被传递给 <code>isExtensible</code>方法。 this 绑定在 handler 对象上。</p>
<dl>
<dt><code>target</code></dt>
<dd>目标对象。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p><code>isExtensible</code>方法必须返回一个 Boolean值或可转换成Boolean的值。</p>
<h2 id="描述">描述</h2>
<p>handler.isExtensible()用于拦截对对象的Object.isExtensible()。</p>
<h3 id="拦截">拦截</h3>
<p>该方法会拦截目标对象的以下操作:</p>
<ul>
<li><a href="Reference/Global_Objects/Object/isExtensible" title="Object.isExtensible() 方法判断一个对象是否是可扩展的（是否可以在它上面添加新的属性）。"><code>Object.isExtensible()</code></a></li>
<li><a href="Reference/Global_Objects/Reflect/isExtensible" title="静态方法 Reflect.isExtensible() 判断一个对象是否可扩展 （即是否能够添加新的属性）。与它 Object.isExtensible() 方法相似，但有一些不同，详情可见 differences。"><code>Reflect.isExtensible()</code></a></li>
</ul>
<h3 id="约束">约束</h3>
<p>如果违背了以下的约束，proxy会抛出 TypeError:</p>
<ul>
<li><code>Object.isExtensible(proxy)</code> 必须同<code>Object.isExtensible(target)</code>返回相同值。也就是必须返回true或者为true的值,返回false和为false的值都会报错。</li>
</ul>
<h2 id="示例">示例</h2>
<p>以下代码演示<a href="Reference/Global_Objects/Object/isExtensible" title="Object.isExtensible() 方法判断一个对象是否是可扩展的（是否可以在它上面添加新的属性）。"><code>Object.isExtensible()</code></a>.</p>
<pre><code  class="language-javascript">var p = new Proxy({}, {
  isExtensible: function(target) {
    console.log('called');
    return true;//也可以return 1;等表示为true的值
  }
});

console.log(Object.isExtensible(p)); // "called"
                                     // true
</code></pre>
<p>以下代码演示违反约束的情况。</p>
<pre><code  class="language-javascript">var p = new Proxy({}, {
  isExtensible: function(target) {
    return false;//return 0;return NaN等都会报错
  }
});

Object.isExtensible(p); // TypeError is thrown
</code></pre>
<h2 id="规范">规范</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><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-proxy-object-internal-methods-and-internal-slots-isextensible" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">[[IsExtensible]]</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-isextensible" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">[[IsExtensible]]</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<div>
<div class="hidden">The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>isExtensible</code></th><td class="bc-supports-unknown bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              31</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-unknown bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              31</td><td class="bc-supports-unknown bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-unknown bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              6.0.0</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
<span>Full support</span>
                  
                </abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
<abbr class="bc-level bc-level-no only-icon" title="No support">
<span>No support</span>
                  
                </abbr></span></dt><dd>No support</dd><dt><span class="bc-supports-unknown bc-supports">
<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
<span>Compatibility unknown</span>
                  
                </abbr></span></dt><dd>Compatibility unknown</dd></dl></section></div><p></p>
</div>
<h2 id="另见">另见</h2>
<ul>
<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>
<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>
<li><a href="Reference/Global_Objects/Object/isExtensible" title="Object.isExtensible() 方法判断一个对象是否是可扩展的（是否可以在它上面添加新的属性）。"><code>Object.isExtensible()</code></a></li>
<li><a href="Reference/Global_Objects/Reflect/isExtensible" title="静态方法 Reflect.isExtensible() 判断一个对象是否可扩展 （即是否能够添加新的属性）。与它 Object.isExtensible() 方法相似，但有一些不同，详情可见 differences。"><code>Reflect.isExtensible()</code></a></li>
</ul>
</article>