---
title: String.length
slug: Web/JavaScript/Reference/Global_Objects/String/length
tags:
  - JavaScript
  - Property
  - Prototype
  - String
translation_of: Web/JavaScript/Reference/Global_Objects/String/length
---
<p>{{JSRef("Global_Objects", "String")}}</p>

<h2 id="Summary" name="Summary">概述</h2>

<p><strong>length</strong> 属性表示一个字符串的长度。</p>

<h2 id="Description" name="Description">描述</h2>

<p>该属性返回字符串中字符编码单元的数量。JavaScript 使用 {{ interwiki("wikipedia", "UTF-16") }} 编码，该编码使用一个 16 比特的编码单元来表示大部分常见的字符，使用两个代码单元表示不常用的字符。因此 length 返回值可能与字符串中实际的字符数量不相同。</p>

<p>空字符串的 <code>length</code> 为 0。</p>

<p>静态属性 <strong>String.length</strong> 返回 1。</p>

<h2 id="Examples" name="Examples">示例</h2>

<pre class="brush: js">var x = "Mozilla";
var empty = "";

console.log("Mozilla is " + x.length + " code units long");
/* "Mozilla is 7 code units long" */

console.log("The empty string is has a length of " + empty.length);
/* "The empty string is has a length of 0" */</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('ES1')}}</td>
   <td>{{Spec2('ES1')}}</td>
   <td>Initial definition. Implemented in JavaScript 1.0.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-15.5.5.1', 'String.prototype.length')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-properties-of-string-instances-length', 'String.prototype.length')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p>{{ CompatibilityTable() }}</p>

<div>
<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>
<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">相关链接</h2>

<ul>
 <li><a class="external external-icon" href="http://developer.teradata.com/blog/jasonstrimpel/2011/11/javascript-string-length-and-internationalizing-web-applications">JavaScript String.length and Internationalizing Web Applications</a></li>
</ul>