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---
title: WindowEventHandlers.onbeforeprint
slug: Web/API/WindowEventHandlers/onbeforeprint
translation_of: Web/API/WindowEventHandlers/onbeforeprint
---
<div>{{ApiRef}}</div>
<div>{{domxref("WindowEventHandlers")}}的<code><strong>onbeforeprint</strong></code>属性是用于处理当前窗口的{{event("beforeprint")}}事件的{{event("Event_handlers", "event handler")}}。在打开打印对话窗口之前会触发这些事件。</div>
<div></div>
<div><font><font>在</font></font><code>beforeprint</code><font><font>和</font></font>{{event("afterprint")}}<font><font>事件允许网页在打印开始前更改他们的内容（例如：可能是删除一个横幅），然后在打印完成后恢复这些更改。通常，您应该更喜欢使用</font></font><code><a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries#Media_types">@media print</a></code><font><font>CSS规则，但是在某些情况下可能有必要使用这些事件。</font></font></div>
<h2 id="语法">语法</h2>
<pre class="syntaxbox notranslate">window.addEventListener("beforeprint", function(event) { ... });
window.onbeforeprint = function(event) { ... };
</pre>
<h2 id="范例">范例</h2>
<p><font><font>Safari没有实现这些事件，但是您可以使用创建与</font></font><code>beforeprint</code><font><font>事件</font><font>等效的结果</font><font>。</font></font>{{domxref("window.matchMedia")}}<code>('print')</code></p>
<pre class="brush: js notranslate">var mediaQueryList = window.matchMedia('print');
mediaQueryList.addListener(function(mql) {
if(mql.matches) {
console.log('webkit equivalent of onbeforeprint');
}
});</pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
<thead>
<tr>
<th scope="col">规范</th>
<th scope="col">状态</th>
<th scope="col">注解</th>
</tr>
</thead>
<tbody>
<tr>
<td>{{SpecName('HTML WHATWG', '#handler-window-onbeforeprint', 'onbeforeprint')}}</td>
<td>{{Spec2('HTML WHATWG')}}</td>
<td></td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{Compat("api.WindowEventHandlers.onbeforeprint")}}</p>
<h2 id="参阅">参阅</h2>
<ul>
<li>{{domxref("Window.print()")}}</li>
<li>{{domxref("WindowEventHandlers.onafterprint")}}</li>
<li><a href="/en-US/docs/Web/Guide/Printing">Printing</a></li>
</ul>
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