---
title: 'Array.prototype[@@unscopables]'
slug: Web/JavaScript/Reference/Global_Objects/Array/@@unscopables
tags:
  - Array
  - ECMAScript 2015
  - JavaScript
  - Property
  - Prototype
translation_of: Web/JavaScript/Reference/Global_Objects/Array/@@unscopables
---
<div>{{JSRef}}</div>

<p>Symbol 属性 <code><strong>@@unscopable</strong></code> 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。这些属性被排除在由 <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>

<h2 id="语法">语法</h2>

<pre class="brush: js"><var>arr</var>[Symbol.unscopables]</pre>

<h2 id="描述">描述</h2>

<p><code>with</code> 绑定中未包含的数组默认属性有：</p>



<ul>
 <li>{{jsxref("Array.prototype.copyWithin()", "copyWithin()")}}</li>
 <li>{{jsxref("Array.prototype.entries()", "entries()")}}</li>
 <li>{{jsxref("Array.prototype.fill()", "fill()")}}</li>
 <li>{{jsxref("Array.prototype.find()", "find()")}}</li>
 <li>{{jsxref("Array.prototype.findIndex()", "findIndex()")}}</li>
 <li>{{jsxref("Array.prototype.includes()", "includes()")}}</li>
 <li>{{jsxref("Array.prototype.keys()", "keys()")}}</li>
 <li>{{jsxref("Array.prototype.values()", "values()")}}</li>
</ul>

<p>参考 {{jsxref("Symbol.unscopables")}} 以了解如何为自定义的对象设置 <code>unscopables</code>。</p>

<p>{{js_property_attributes(0,0,1)}}</p>

<h2 id="示例">示例</h2>

<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 {{jsxref("Array.prototype.keys()")}} 这个方法。这意味着在 <code>with</code> 语句的作用域中，"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 <code>with</code> 语句的作用域内。</p>

<pre class="brush: js">var keys = [];

with(Array.prototype) {
  keys.push("something");
}

Object.keys(Array.prototype[Symbol.unscopables]);
// ["copyWithin", "entries", "fill", "find", "findIndex",
//  "includes", "keys", "values"]</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">规范名称</th>
   <th scope="col">规范状态</th>
   <th scope="col">备注</th>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-array.prototype-@@unscopables', 'Array.prototype[@@unscopables]')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>首次定义</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-array.prototype-@@unscopables', 'Array.prototype[@@unscopables]')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div>


<p>{{Compat("javascript.builtins.Array.@@unscopables")}}</p>
</div>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{jsxref("Symbol.unscopables")}}</li>
</ul>