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---
title: Headers.get()
slug: Web/API/Headers/get
tags:
- get()
translation_of: Web/API/Headers/get
---
<p>{{APIRef("Fetch")}}{{ SeeCompatTable() }}</p>
<p><strong><code>get()</code></strong> 方法以 {{domxref("ByteString")}} 形式从Headers对象中返回指定header的全部值. 如果Header对象中不存在请求的header,则返回 <code>null</code>.</p>
<div class="note">
<p><strong>Note:</strong>出于安全原因, 部分头信息只能被用户代理控制. 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>
</div>
<h2 id="Syntax">Syntax</h2>
<pre class="brush: js">myHeaders.get(name);</pre>
<h3 id="Parameters">Parameters</h3>
<dl>
<dt><em>name</em></dt>
<dd>从Headers对象中检索的HTTP header 名,如果HTTP header中不存在指定header名则会抛出一个{{jsxref("TypeError")}}.</dd>
</dl>
<h3 id="Returns">Returns</h3>
<p>以 {{domxref("ByteString")}} 形式返回检索到的值.</p>
<h2 id="Example">Example</h2>
<p>创建一个空的Headers对象:</p>
<pre class="brush: js">var myHeaders = new Headers(); // Currently empty</pre>
<p>可以通过get()方法来获取header中的值:</p>
<pre class="brush: js">myHeaders.append('Content-Type', 'image/jpeg');
myHeaders.get('Content-Type'); // Returns 'image/jpeg'
</pre>
<p>如果存在多个header值,那么只有第一个值会被返回:</p>
<pre class="brush: js">myHeaders.append('Accept-Encoding', 'deflate');
myHeaders.append('Accept-Encoding', 'gzip');
myHeaders.get('Accept-Encoding'); // Returns <code>"deflate,gzip"</code>
</pre>
<div class="note">
<p><strong>Note</strong>: {{domxref("Headers.getAll")}} used to have this functionality, with {{domxref("Headers.get")}} returning only the first value added to the <code>Headers</code> object. The latest spec has removed <code>getAll()</code>, and updated <code>get()</code> to return all values.</p>
</div>
<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-get','get()')}}</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>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>{{ 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>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>{{ 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>
|
