---
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>