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---
title: RegExp.lastIndex
slug: Web/JavaScript/Reference/Global_Objects/RegExp/lastIndex
tags:
- JavaScript
- Property
- RegExp
- Regular Expressions
translation_of: Web/JavaScript/Reference/Global_Objects/RegExp/lastIndex
---
<div>
{{JSRef("Global_Objects", "RegExp")}}</div>
<h2 id="Summary" name="Summary" style="margin-bottom: 20px; line-height: 30px;">概述</h2>
<p><code><strong>lastIndex</strong></code> 是正则表达式的一个可读可写的整型属性，用来指定下一次匹配的起始索引。</p>
<div>
{{js_property_attributes(1,0,0)}}</div>
<h2 id="语法" style="margin-bottom: 20px; line-height: 30px;">语法</h2>
<pre class="syntaxbox language-html" style="margin-bottom: 0px; padding: 1em; border-left-width: 6px; border-left-style: solid; font-family: Consolas, Monaco, 'Andale Mono', monospace; font-size: 14px; direction: ltr; white-space: normal; text-shadow: none; background-color: rgba(212, 221, 228, 0.498039);"><var>lastIndex</var> = <var>regExpObj</var>.lastIndex;</pre>
<h2 id="Description" name="Description" style="margin-bottom: 20px; line-height: 30px;">描述</h2>
<p>只有正则表达式使用了表示全局检索的 "<code>g</code>" 标志时，该属性才会起作用。此时应用下面的规则：</p>
<ul>
<li>如果 <code>lastIndex</code> 大于字符串的长度，则 <code>regexp.test</code> 和 <code>regexp.exec</code> 将会匹配失败，然后 <code>lastIndex</code> 被设置为 0。</li>
<li>如果 <code>lastIndex</code> 等于字符串的长度，且该正则表达式匹配空字符串，则该正则表达式匹配从 <code>lastIndex</code> 开始的字符串。（then the regular expression matches input starting at <code style="font-style: normal;">lastIndex</code>.）</li>
<li>如果 <code>lastIndex</code> 等于字符串的长度，且该正则表达式不匹配空字符串 ，则该正则表达式不匹配字符串，<code>lastIndex</code> 被设置为 0.。</li>
<li>否则，<code>lastIndex</code> 被设置为紧随最近一次成功匹配的下一个位置。</li>
</ul>
<h2 id="示例" style="margin-bottom: 20px; line-height: 30px;">示例</h2>
<p>考虑下面的语句：</p>
<pre class="brush: js">var re = /(hi)?/g;</pre>
<div class="line-number" style="margin-top: 1em; position: absolute; left: 0px; right: 0px; line-height: inherit; top: 0px; background: 0px 0px;">
</div>
<p>匹配空字符串</p>
<pre class="brush: js">console.log(re.exec("hi"));
console.log(re.lastIndex);</pre>
<div class="line-number" style="margin-top: 1em; position: absolute; left: 0px; right: 0px; line-height: inherit; top: 0px; background: 0px 0px;">
</div>
<div class="line-number" style="margin-top: 1em; position: absolute; left: 0px; right: 0px; line-height: inherit; top: 19px; background: 0px 0px;">
</div>
<p>返回 <code>["hi", "hi"]</code> ，<code>lastIndex</code> 等于 2。</p>
<pre class="brush: js">console.log(re.exec("hi"));
console.log(re.lastIndex);</pre>
<div class="line-number" style="margin-top: 1em; position: absolute; left: 0px; right: 0px; line-height: inherit; top: 0px; background: 0px 0px;">
</div>
<div class="line-number" style="margin-top: 1em; position: absolute; left: 0px; right: 0px; line-height: inherit; top: 19px; background: 0px 0px;">
</div>
<p>返回 <code>["", undefined]</code>，即一个数组，其第 0 个元素为匹配的字符串。此种情况下为空字符串，是因为 <code>lastIndex</code> 为 2（且一直是 2），"<code>hi</code>" 长度为 2。</p>
<h2 id="规范" style="margin-bottom: 20px; line-height: 30px;">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>ECMAScript 3rd Edition. Implemented in JavaScript 1.2.</td>
<td>Standard</td>
<td>Initial definition.<br>
JavaScript 1.5: <code>lastIndex</code> is a property of a <code>RegExp</code> instance, not the <code>RegExp</code> object.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-15.10.7.5', 'RegExp.lastIndex')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-properties-of-regexp-instances', 'RegExp.lastIndex')}}</td>
<td>{{Spec2('ES6')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性" style="margin-bottom: 20px; line-height: 30px;">浏览器兼容性</h2>
<p>{{ CompatibilityTable() }}</p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th style="line-height: 16px;">Feature</th>
<th style="line-height: 16px;">Chrome</th>
<th style="line-height: 16px;">Firefox (Gecko)</th>
<th style="line-height: 16px;">Internet Explorer</th>
<th style="line-height: 16px;">Opera</th>
<th style="line-height: 16px;">Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th style="line-height: 16px;">Feature</th>
<th style="line-height: 16px;">Android</th>
<th style="line-height: 16px;">Chrome for Android</th>
<th style="line-height: 16px;">Firefox Mobile (Gecko)</th>
<th style="line-height: 16px;">IE Mobile</th>
<th style="line-height: 16px;">Opera Mobile</th>
<th style="line-height: 16px;">Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also" name="See_also" style="margin-bottom: 20px; line-height: 30px;">相关链接</h2>
<ul>
<li>{{jsxref("RegExp.prototype.ignoreCase")}}</li>
<li>{{jsxref("RegExp.prototype.global")}}</li>
<li>{{jsxref("RegExp.prototype.multiline")}}</li>
<li>{{jsxref("RegExp.prototype.source")}}</li>
<li>{{jsxref("RegExp.prototype.sticky")}}</li>
</ul>
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