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---
title: ResizeObserver.observe()
slug: Web/API/ResizeObserver/observe
translation_of: Web/API/ResizeObserver/observe
---
<div>{{APIRef("Resize Observer API")}}{{SeeCompatTable}}</div>
<p class="summary">The <strong><code>observe()</code></strong> method of the {{domxref("ResizeObserver")}} interface initiates observing of a specified {{domxref('Element')}} or {{domxref('SVGElement')}}.<br>
{{domxref("ResizeObserver")}} 接口的 <strong><code>observe()</code> </strong>方法用于观察一个指定{{domxref('Element')}} 或 {{domxref('SVGElement')}}。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox"><em>resizeObserver</em>.observe(<em>target</em>);</pre>
<h3 id="参数">参数</h3>
<dl>
<dt>target</dt>
<dd>被观察的 {{domxref('Element')}} 或 {{domxref('SVGElement')}} 引用。</dd>
<dt>options {{optional_inline}}</dt>
<dd>一个指定观察设置的可选参数对象。目前只有一个可设置的选项：
<dl>
<dt><code>box</code></dt>
<dd>设置观察者将以哪种盒子模型来观察变动。可以设置的值为
<code>content-box</code> (默认值)，<code>border-box</code>，和
<code>device-pixel-content-box</code>。</dd>
</dl>
</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>{{jsxref('undefined')}}</p>
<h3 id="异常">异常</h3>
<p>无</p>
<h2 id="示例">示例</h2>
<p>以下示例通过观察box的尺寸变化从而改变其边框圆角半径。</p>
<pre class="brush: js">const resizeObserver = new ResizeObserver(entries => {
for (let entry of entries) {
entry.target.style.borderRadius = Math.max(0, 250 - entry.contentRect.width) + 'px';
}
});
resizeObserver.observe(document.querySelector('.box:nth-child(2)'));</pre>
<h2 id="规范">规范</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('Resize Observer','#dom-resizeobserver-observe','observe()')}}</td>
<td>{{Spec2('Resize Observer')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{Compat("api.ResizeObserver.observe")}}</p>
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