---
title: KeyboardEvent.altKey
slug: Web/API/KeyboardEvent/altKey
tags:
  - API
  - DOM
  - KeyboardEvent
  - events
  - 鼠标事件
translation_of: Web/API/KeyboardEvent/altKey
---
<p id="Summary">{{APIRef("DOM Events")}}</p>

<p><strong><code>KeyboardEvent.altKey</code></strong> 只读属性返回一个 {{jsxref("Boolean")}} 值，表示事件触发时 <kbd>alt</kbd> 键 (OS X系统上的 <kbd>Option</kbd> 或 <kbd>⌥</kbd> 键) 是 (<code>true</code>) 否 (<code>false</code>) 被按下。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">var <em>altKeyPressed</em> = <em>instanceOfKeyboardEvent</em>.altKey
</pre>

<h3 id="返回值">返回值</h3>

<p>布尔值</p>

<h2 id="示例">示例</h2>

<pre class="brush: js">&lt;html&gt;
&lt;head&gt;
&lt;title&gt;altKey example&lt;/title&gt;

&lt;script type="text/javascript"&gt;

function showChar(e){
  alert(
    "Key Pressed: " + String.fromCharCode(e.charCode) + "\n"
    + "charCode: " + e.charCode + "\n"
    + "ALT key pressed: " + e.altKey + "\n"
  );
}

&lt;/script&gt;
&lt;/head&gt;

&lt;body onkeypress="showChar(event);"&gt;
&lt;p&gt;
Press any character key,
with or without holding down the ALT key.&lt;br /&gt;
You can also use the SHIFT key together with the ALT key.
&lt;/p&gt;
&lt;/body&gt;
&lt;/html&gt;</pre>

<h2 id="标准">标准</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('DOM3 Events','#widl-KeyboardEvent-altKey','KeyboardEvent.altkey')}}</td>
   <td>{{Spec2('DOM3 Events')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility" name="Browser_compatibility">浏览器兼容性</h2>

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

<div id="compat-desktop">特性
<table class="compat-table">
 <tbody>
  <tr>
   <th>Edge</th>
   <th>Firefox (Gecko)</th>
   <th>Chrome</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>基本支持</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown()}}</td>
   <td>{{CompatVersionUnknown()}}</td>
   <td>{{CompatVersionUnknown()}}</td>
   <td>{{CompatVersionUnknown()}}</td>
   <td>{{CompatVersionUnknown()}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">特性
<table class="compat-table">
 <tbody>
  <tr>
   <th>Edge</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>Android</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>基本支持</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_also" name="See_also">参考</h2>

<ul>
 <li>{{ domxref("KeyboardEvent") }}</li>
</ul>