---
title: XMLHttpRequest.setRequestHeader()
slug: Web/API/XMLHttpRequest/setRequestHeader
tags:
  - Reference
  - XMLHttpRequests
translation_of: Web/API/XMLHttpRequest/setRequestHeader
---
<p>{{APIRef('XMLHttpRequest')}}</p>

<p><strong>XMLHttpRequest.setRequestHeader()</strong> 是设置HTTP请求头部的方法。此方法必须在  {{domxref("XMLHttpRequest.open", "open()")}} 方法和 {{domxref("XMLHttpRequest.send", "send()")}}   之间调用。如果多次对同一个请求头赋值，只会生成一个合并了多个值的请求头。</p>

<p>如果没有设置 {{HTTPHeader("Accept")}} 属性，则此发送出{{domxref("XMLHttpRequest.send", "send()")}} 的值为此属性的默认值<code>*/*</code> 。</p>

<p>安全起见，有些请求头的值只能由user agent设置：{{Glossary("Forbidden_header_name", "forbidden header names", 1)}}和{{Glossary("Forbidden_response_header_name", "forbidden response header names", 1)}}.</p>

<div class="note">
<p>自定义一些header属性进行跨域请求时，可能会遇到"<strong>not allowed by Access-Control-Allow-Headers in preflight response</strong>"，你可能需要在你的服务端设置"Access-Control-Allow-Headers"。</p>
</div>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">myReq.setRequestHeader(<var>header</var>, <var>value</var>);
</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><code>header</code></dt>
 <dd>属性的名称。</dd>
 <dt><code>value</code></dt>
 <dd>属性的值。</dd>
</dl>

<h2 id="说明">说明</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('XMLHttpRequest', '#the-setRequestHeader()-method', 'setRequestHeader()')}}</td>
   <td>{{Spec2('XMLHttpRequest')}}</td>
   <td>WHATWG living standard</td>
  </tr>
 </tbody>
</table>

<h2 id="兼容性">兼容性</h2>

<div>{{CompatibilityTable}}</div>

<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(1)}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatIe('5')}}<sup>[1]</sup><br>
    {{CompatIe('7')}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatSafari('1.2')}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatUnknown}}</td>
   <td>1.0</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] 使用ActiveXObject()实现的。Internet Explorer 7之后使用的是标准的XMLHttpRequest。</p>

<h2 id="参考">参考</h2>

<p><a href="/zh-CN/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest">使用XMLHttpRequest</a></p>