Revision 530055 of regexp.lastIndex

<div>
 {{JSRef("Global_Objects", "RegExp")}}</div>
<h2 id="Summary" name="Summary">Summary</h2>
<p>The <code><strong>lastIndex</strong></code> is a read/write integer property of regular expressions that specifies the index at which to start the next match.</p>
<div>
 {{js_property_attributes(1,0,0)}}</div>
<h2 id="Syntax">Syntax</h2>
<pre class="syntaxbox">
<var>lastIndex</var> = <var>regExpObj</var>.lastIndex;
</pre>
<h2 id="Description" name="Description">Description</h2>
<p>This property is set only if the regular expression used the "<code>g</code>" flag to indicate a global search. The following rules apply:</p>
<ul>
 <li>If <code>lastIndex</code> is greater than the length of the string, <code>regexp.test</code> and <code>regexp.exec</code> fail, then&nbsp;<code>lastIndex</code> is set to 0.</li>
 <li>If <code>lastIndex</code> is equal to the length of the string and if the regular expression matches the empty string, then the regular expression matches input starting at <code>lastIndex</code>.</li>
 <li>If <code>lastIndex</code> is equal to the length of the string and if the regular expression does not match the empty string, then the regular expression mismatches input, and <code>lastIndex</code> is reset to 0.</li>
 <li>Otherwise, <code>lastIndex</code> is set to the next position following the most recent match.</li>
</ul>
<h2 id="Examples">Examples</h2>
<p>Consider the following sequence of statements:</p>
<pre class="brush:js">
var re = /(hi)?/g;
</pre>
<p>Matches the empty string.</p>
<pre class="brush:js">
console.log(re.exec("hi"));
console.log(re.lastIndex);</pre>
<p>Returns <code>\"hi\"</code> with <code>lastIndex</code> equal to 2.</p>
<pre class="brush:js">
console.log(re.exec("hi"));
console.log(re.lastIndex);
</pre>
<p>Returns <code>[\"\"]</code>, an empty array whose zeroth element is the match string. In this case, the empty string because <code>lastIndex</code> was 2 (and still is 2) and "<code>hi</code>" has length 2.</p>
<h2 id="Specifications">Specifications</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>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-properties-of-regexp-instances', 'RegExp.lastIndex')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<p>{{ CompatibilityTable() }}</p>
<div id="compat-desktop">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Chrome</th>
    <th>Firefox (Gecko)</th>
    <th>Internet Explorer</th>
    <th>Opera</th>
    <th>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>Feature</th>
    <th>Android</th>
    <th>Chrome for Android</th>
    <th>Firefox Mobile (Gecko)</th>
    <th>IE Mobile</th>
    <th>Opera Mobile</th>
    <th>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">See also</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>