---
title: FormData.has()
slug: Web/API/FormData/has
translation_of: Web/API/FormData/has
---
<p>{{APIRef("XMLHttpRequest")}}</p>

<p><code><strong>has()</strong></code>方法会返回一个布尔值，表示该{{domxref("FormData")}}对象是否含有某个key 。</p>

<div class="note">
<p><span style="font-size: 14px;"><strong>注意</strong></span>: 该方法在 <a href="/en-US/docs/Web/API/Web_Workers_API">Web Workers</a> 可用。</p>
</div>

<h2 id="语法">语法</h2>

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

<h3 id="append()_Parameters" name="append()_Parameters">参数</h3>

<dl>
 <dt><code>name</code></dt>
 <dd>一个 {{domxref("USVString")}} ，要查询的 key 名称。</dd>
</dl>

<h3 id="返回">返回</h3>

<p>一个 {{domxref("Boolean")}}。</p>

<h2 id="示例">示例</h2>

<p>下列代码会先创建一个空的 formData 对象：</p>

<pre class="brush: js">var formData = new FormData();</pre>

<p>下列代码用来检测 <code>FormData对象是否存在</code><code>username这个key。默认检测一次，使用 </code>{{domxref("FormData.append")}} 插入<code>username之后再检测一次：</code></p>

<pre class="brush: js">formData.has('username'); // Returns false
formData.append('username', 'Chris');
formData.has('username'); // Returns true

</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">规范</th>
   <th scope="col">状态</th>
   <th scope="col">说明</th>
  </tr>
  <tr>
   <td>{{SpecName('XMLHttpRequest','#dom-formdata-has','has()')}}</td>
   <td>{{Spec2('XMLHttpRequest')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</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</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatChrome(50.0)}}</td>
   <td>{{CompatGeckoDesktop("39.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatNo}}</td>
  </tr>
  <tr>
   <td>Available in web workers</td>
   <td>{{CompatChrome(50.0)}}</td>
   <td>{{CompatGeckoDesktop("39.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatVersionUnknown}}</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>Android Webview</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>Firefox OS (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
   <th>Chrome for Android</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatChrome(50.0)}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatNo}}</td>
   <td>
    <p>{{CompatVersionUnknown}}</p>
   </td>
   <td>{{CompatNo}}</td>
   <td>{{CompatChrome(50.0)}}</td>
  </tr>
  <tr>
   <td>Available in web workers</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatChrome(50.0)}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatChrome(50.0)}}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{domxref("XMLHTTPRequest")}}</li>
 <li><a href="/en-US/docs/DOM/XMLHttpRequest/Using_XMLHttpRequest" title="Using XMLHttpRequest">Using XMLHttpRequest</a></li>
 <li><a href="/en-US/docs/DOM/XMLHttpRequest/FormData/Using_FormData_Objects" title="DOM/XMLHttpRequest/FormData/Using_FormData_objects">Using FormData objects</a></li>
 <li>{{HTMLElement("Form")}}</li>
</ul>