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110 lines
9.3 KiB
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<article id="wikiArticle">
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<div></div>
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<p>Symbol属性 @@unscopable 包含了所有 ES2015 (ES6) 中新定义的且并未被更早的 ECMAScript 标准收纳的属性名。这些属性并不包含在 <code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with">with</a></code> 语句绑定的环境中</p>
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<h2 id="语法">语法</h2>
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<pre><code class="language-javascript"><var>arr</var>[Symbol.unscopables]</code></pre>
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<h2 id="描述">描述</h2>
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<p><code>with</code> 绑定中未包含的数组默认属性有：copyWithin, entries, fill, find, findIndex, includes, keys 和 values。</p>
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<p>查看 <a href="Reference/Global_Objects/Symbol/unscopables" title="Symbol.unscopables 指用于指定对象值，其对象自身和继承的从关联对象的 with 环境绑定中排除的属性名称。"><code>Symbol.unscopables</code></a> 以了解如何给你定义的对象设置 unscopables。</p>
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<p></p><table class="standard-table">
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<thead>
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<tr>
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<th class="header" colspan="2"><code>Array.prototype[@@unscopables]</code> 属性的属性特性：</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>writable</td>
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<td>false</td>
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</tr>
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<tr>
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<td>enumerable</td>
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<td>false</td>
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</tr>
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<tr>
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<td>configurable</td>
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<td>true</td>
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</tr>
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</tbody>
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</table><p></p>
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<h2 id="示例">示例</h2>
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<p>以下的代码在 ES5 或更早的版本中能正常工作。然而 ECMAScript 2015 (ES6) 或之后的版本中新添加了 <a href="Reference/Global_Objects/Array/keys" title="keys() 方法返回一个包含数组中每个索引键的Array Iterator对象。"><code>Array.prototype.keys()</code></a> 这个方法。这意味着在 <code>with</code> 语句的作用域，"keys"只能作为方法而不能作为某个变量。这正是内置的 <code>@@unscopables</code> 即 <code>Array.prototype[@@unscopables]</code> symbol属性所要解决的问题：防止某些数组方法被添加到 with 语句的作用域内。</p>
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<pre><code class="language-javascript">var keys = [];
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with(Array.prototype) {
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keys.push("something");
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}
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Object.keys(Array.prototype[Symbol.unscopables]);
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// ["copyWithin", "entries", "fill", "find", "findIndex",
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// "includes", "keys", "values"]</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">规范名称</th>
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<th scope="col">规范状态</th>
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<th scope="col">备注</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-array.prototype-@@unscopables" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Array.prototype[@@unscopables]</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>首次定义</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-array.prototype-@@unscopables" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Array.prototype[@@unscopables]</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>
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<div class="hidden">The compatibility table in 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>
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<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>@@unscopables</code></th><td class="bc-supports-unknown bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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12</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">
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<span>Full support</span>
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</abbr>
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48</td><td class="bc-supports-unknown bc-browser-ie"><span class="bc-browser-name">IE</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></td><td class="bc-supports-unknown bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></td><td class="bc-supports-unknown bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr title="Compatibility unknown; please update this.">
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?
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</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.">
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?
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</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.">
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?
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</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.">
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?
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</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">
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<span>Full support</span>
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</abbr>
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48</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.">
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?
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</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.">
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?
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</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.">
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?
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</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">
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<span>Full support</span>
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</abbr>
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0.12</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">
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<abbr class="bc-level bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-unknown bc-supports">
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<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
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<span>Compatibility unknown</span>
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</abbr></span></dt><dd>Compatibility unknown</dd></dl></section></div><p></p>
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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/Symbol/unscopables" title="Symbol.unscopables 指用于指定对象值，其对象自身和继承的从关联对象的 with 环境绑定中排除的属性名称。"><code>Symbol.unscopables</code></a></li>
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</ul>
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</article> |