files/zh-cn/web/api/xpathevaluator/index.html


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---
title: XPathEvaluator
slug: Web/API/XPathEvaluator
tags:
  - API
  - DOM
  - DOM XPath API
  - Document
  - Interface
  - NeedsTranslation
  - Reference
  - TopicStub
  - XML
  - XPath
  - XPathEvaluator
translation_of: Web/API/XPathEvaluator
---
<p>{{APIRef("DOM XPath")}}</p>

<p> <code>XPathEvaluator</code>  接口能够对 {{Glossary("XPath")}} 表达式进行编译和求值。</p>

<p>该接口实现自{{domxref("Document")}}的接口。</p>

<h2 id="Methods" name="Methods">方法</h2>

<dl>
 <dt>{{DOMxRef("XPathEvaluator.createExpression()")}}</dt>
 <dd>创建一个解析过的XPath和解析后的namespaces</dd>
 <dt>{{DOMxRef("XPathEvaluator.createNSResolver()")}}</dt>
 <dd>任意DOM节点能够通过该方法来解析namespaces，允许通过节点出现在文档中的相对上下文对XPath表达式进行求值。</dd>
 <dt>{{DOMxRef("XPathEvaluator.evaluate()")}}</dt>
 <dd>对XPath字符串求值，返回可能的确切类型的匹配结果。</dd>
</dl>

<h2 id="例子">例子</h2>

<p>下面的实例展示了如何使用<code>XPathEvaluator</code>接口。</p>

<h3 id="HTML">HTML</h3>

<pre class="brush: html">&lt;div&gt;XPath example&lt;/div&gt;
&lt;div&gt;Number of &amp;lt;div&amp;gt;s: &lt;output&gt;&lt;/output&gt;&lt;/div&gt;
</pre>

<h3 id="JavaScript">JavaScript</h3>

<pre class="brush: js">var xpath = "//div";
var evaluator = new XPathEvaluator();
var expression = evaluator.createExpression("//div");
var result = expression.evaluate(document, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE);
document.querySelector("output").textContent = result.snapshotLength;
</pre>

<h3 id="结果"> 结果</h3>


<p>{{EmbedLiveSample('Example', 400, 70)}}</p>

<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("DOM3 XPath", "xpath.html#XPathEvaluator", "XPathEvaluator")}}</td>
   <td>{{Spec2("DOM3 XPath")}}</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.XPathEvaluator")}}</p>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{domxref("document.createExpression()")}}</li>
 <li>{{domxref("XPathExpression")}}</li>
</ul>