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---
title: Array.prototype.keys()
slug: Web/JavaScript/Reference/Global_Objects/Array/keys
tags:
- Array
- ECMAScript 2015
- Iterator
- JavaScript
- Method
- Prototype
translation_of: Web/JavaScript/Reference/Global_Objects/Array/keys
---
<div>{{JSRef}}</div>
<p><code><strong>keys()</strong></code> 方法會回傳一個包含陣列中的每一個索引之鍵（keys）的新 <code><strong>Array Iterator</strong></code> 物件。</p>
<div>{{EmbedInteractiveExample("pages/js/array-keys.html")}}</div>
<h2 id="語法">語法</h2>
<pre class="syntaxbox"><var>arr</var>.keys()</pre>
<h3 id="回傳值">回傳值</h3>
<p>一個新的 {{jsxref("Array")}} 迭代器（iterator）物件。</p>
<h2 id="範例">範例</h2>
<h3 id="鍵迭代器不會乎略陣列中的空元素">鍵迭代器不會乎略陣列中的空元素</h3>
<pre class="brush: js">var arr = ['a', , 'c'];
var sparseKeys = Object.keys(arr);
var denseKeys = [...arr.keys()];
console.log(sparseKeys); // ['0', '2']
console.log(denseKeys); // [0, 1, 2]
</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('ES2015', '#sec-array.prototype.keys', 'Array.prototype.keys')}}</td>
<td>{{Spec2('ES2015')}}</td>
<td>Initial definition.</td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-array.prototype.keys', 'Array.prototype.keys')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
<div>
<p>{{Compat("javascript.builtins.Array.keys")}}</p>
</div>
<h2 id="參見">參見</h2>
<ul>
<li>{{jsxref("Array.prototype.values()")}}</li>
<li>{{jsxref("Array.prototype.entries()")}}</li>
<li><a href="/zh-TW/docs/Web/JavaScript/Reference/Iteration_protocols">迭代協議</a></li>
</ul>
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