---
title: Storage.key()
slug: Web/API/Storage/key
translation_of: Web/API/Storage/key
---
<p>{{APIRef()}}</p>

<p><code>key()</code> 作为 {{domxref("Storage")}} 接口的方法，接受一个数值 n 作为参数，返回存储对象第 n 个数据项的键名。键的存储顺序是由用户代理定义的，所以尽可能不要依赖这个方法。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox notranslate">var <em>aKeyName</em> = <em>storage</em>.key(<em>key</em>);</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><em>key</em></dt>
 <dd>一个整数，表示要获取的键名索引。</dd>
</dl>

<h3 id="返回值">返回值</h3>

<p>一个包含键名的 {{domxref("DOMString")}}。</p>

<h2 id="示例">示例</h2>

<p>下面的函数添加三个数据项到当前域名的本地存储里，然后返回第三个的键名：</p>

<pre class="brush: js notranslate">function populateStorage() {
  localStorage.setItem('bgcolor', 'yellow');
  localStorage.setItem('font', 'Helvetica');
  localStorage.setItem('image', 'cats.png');

  localStorage.key(2); // 应该返回 'image'
}</pre>

<div class="note">
<p><strong>备注：</strong> 关于实际的例子，可以查看 <a href="https://github.com/mdn/dom-examples/tree/master/web-storage">Web Storage Demo</a>.</p>
</div>

<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>{{SpecName('Web Storage', '#dom-storage-key', 'key()')}}</td>
   <td>{{Spec2('Web Storage')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p>{{ CompatibilityTable() }}</p>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari (WebKit)</th>
  </tr>
  <tr>
   <td>localStorage</td>
   <td>4</td>
   <td>3.5</td>
   <td>8</td>
   <td>10.50</td>
   <td>4</td>
  </tr>
  <tr>
   <td>sessionStorage</td>
   <td>5</td>
   <td>2</td>
   <td>8</td>
   <td>10.50</td>
   <td>4</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Phone</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>2.1</td>
   <td>{{ CompatUnknown }}</td>
   <td>8</td>
   <td>11</td>
   <td>iOS 3.2</td>
  </tr>
 </tbody>
</table>
</div>

<p>各浏览器支持的 localStorage 和 sessionStorage 容量不同。测试页面：<a class="external" href="http://dev-test.nemikor.com/web-storage/support-test/" title="http://dev-test.nemikor.com/web-storage/support-test/">detailed rundown of all the storage capacities for various browsers</a>.</p>

<div class="note">
<p><strong>Note: </strong>since iOS 5.1, Safari Mobile stores localStorage data in the cache folder, which is subject to occasional clean up, at the behest of the OS, typically if space is short.</p>
</div>

<h2 id="相关链接">相关链接</h2>

<p><a href="/zh-CN/docs/Web/API/Web_Storage_API/Using_the_Web_Storage_API">使用 Web Storage API</a></p>