---
title: Headers.has()
slug: Web/API/Headers/has
translation_of: Web/API/Headers/has
---
<div>{{APIRef("Fetch")}}</div>

<p>{{domxref("Headers")}} 接口的 <strong><code>has()</code></strong>方法返回一个布尔值来声明一个 <code>Headers</code>对象 是否包含特定的头信息.</p>

<p>考虑到安全因素, 一些头信息只能被user agent来管理. 这些头信息包括{{Glossary("Forbidden_header_name", "forbidden header names", 1)}}  和{{Glossary("Forbidden_response_header_name", "forbidden response header names", 1)}}.</p>

<h2 id="Syntax">Syntax</h2>

<pre class="brush: js">myHeaders.has(name);</pre>

<h3 id="Parameters">Parameters</h3>

<dl>
 <dt><em>name</em></dt>
 <dd>你要测试的HTTP头字段的名称。如果给出的名称不在HTTP头中，将爬出异常{{jsxref("TypeError")}}。</dd>
</dl>

<h3 id="Returns">Returns</h3>

<p>A {{domxref("Boolean")}}.</p>

<h2 id="Example">Example</h2>

<p>创建一个空的Headers对象是简单的:</p>

<pre class="brush: js">var myHeaders = new Headers(); // Currently empty</pre>

<p>你可以使用{{domxref("Headers.append")}}来向myHeaders添加一个头信息, 然后使用 <code>has()方法来测试是否添加成功</code>:</p>

<pre class="brush: js">myHeaders.append('Content-Type', 'image/jpeg');
myHeaders.has('Content-Type'); // Returns true
myHeaders.has('Accept-Encoding'); // Returns false
</pre>

<h2 id="Specifications">Specifications</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('Fetch','#dom-headers-has','has()')}}</td>
   <td>{{Spec2('Fetch')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

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

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Edge</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari (WebKit)</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{ CompatChrome(42) }}<br>
    {{ CompatChrome(41) }} behind pref<br>
     </td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{ CompatGeckoDesktop(39)}}<br>
    34 behind pref</td>
   <td>{{ CompatNo }}</td>
   <td>
    <p>29<br>
     28 behind pref</p>
   </td>
   <td>{{ CompatNo }}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Edge</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>Firefox OS (Gecko)</th>
   <th>IE Phone</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
   <th>Chrome for Android</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{ CompatNo }}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{ CompatNo }}</td>
   <td>{{ CompatNo }}</td>
   <td>{{ CompatNo }}</td>
   <td>{{ CompatNo }}</td>
   <td>{{ CompatNo }}</td>
   <td>{{ CompatNo }}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/API/ServiceWorker_API">ServiceWorker API</a></li>
 <li><a href="/en-US/docs/Web/HTTP/Access_control_CORS">HTTP access control (CORS)</a></li>
 <li><a href="/en-US/docs/Web/HTTP">HTTP</a></li>
</ul>