files/zh-cn/web/api/mediadevices/getsupportedconstraints/index.html


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---
title: MediaDevices.getSupportedConstraints()
slug: Web/API/MediaDevices/getSupportedConstraints
translation_of: Web/API/MediaDevices/getSupportedConstraints
---
<p>{{APIRef("Media Capture and Streams")}}</p>

<p> </p>

<p>{{domxref("MediaDevices")}} 接口的<code><strong>getSupportedConstraints</strong></code><strong><code>()</code></strong>方法返回一个基于{{domxref("MediaTrackSupportedConstraints")}}的对象, 其成员字段都是客户端（{{Glossary("user agent")}}）所支持的约束属性（如帧率，窗口大小）。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">var <em>supportedConstraints</em> = navigator.mediaDevices.getSupportedConstraints();</pre>

<h3 id="参数">参数</h3>

<p>无</p>

<h3 id="返回值">返回值</h3>

<p>一个新的基于{{domxref("MediaTrackSupportedConstraints")}} 的对象用来监视客户端所支持的约束属性.因为只有客户端所支持的约束属性才能被展示在这个列表中 , 这些布尔值（Boolean）属性的每一个都为true。</p>

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

<p>这个示例展示了你的客户端所支持的约束属性的列表。</p>

<div class="hidden">
<h3 id="HTML_内容">HTML 内容</h3>

<pre class="brush: html">&lt;p&gt;The following media constraints are supported by your browser:&lt;/p&gt;

&lt;ul id="constraintList"&gt;
&lt;/ul&gt;</pre>

<h3 id="CSS_内容">CSS 内容</h3>

<pre class="brush: css">body {
  font: 15px Arial, sans-serif;
}</pre>

<h3 id="JavaScript_内容">JavaScript 内容</h3>
</div>

<pre class="brush: js">let constraintList = document.getElementById("constraintList");
let supportedConstraints = navigator.mediaDevices.getSupportedConstraints();

for (let constraint in supportedConstraints) {
  if (supportedConstraints.hasOwnProperty(constraint)) {
    let elem = document.createElement("li");

    elem.innerHTML = "&lt;code&gt;" + constraint + "&lt;/code&gt;";
    constraintList.appendChild(elem);
  }
}</pre>

<h3 id="结果">结果</h3>

<p>{{ EmbedLiveSample('Example', 600, 350) }}</p>

<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">备注</th>
  </tr>
  <tr>
   <td>{{SpecName('Media Capture', '#widl-MediaDevices-getSupportedConstraints-MediaTrackSupportedConstraints', 'getSupportedConstraints()')}}</td>
   <td>{{Spec2('Media Capture')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器支持情况">浏览器支持情况</h2>

{{Compat("api.MediaDevices.getSupportedConstraints")}}