---
title: String.prototype.toLowerCase()
slug: Web/JavaScript/Reference/Global_Objects/String/toLowerCase
tags:
  - JavaScript
  - Method
  - Prototype
  - String
  - toLowerCase()
translation_of: Web/JavaScript/Reference/Global_Objects/String/toLowerCase
---
<div>{{JSRef}}</div>

<p><code><strong>toLowerCase()</strong></code> 会将调用该方法的字符串值转为小写形式，并返回。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox  language-html"><code class="language-html">str.toLowerCase()</code>
</pre>

<h3 id="返回值">返回值</h3>

<p>一个新的字符串，表示转换为小写的调用字符串。</p>

<h2 id="描述">描述</h2>

<p><code>toLowerCase</code> 会将调用该方法的字符串值转为小写形式，并返回。<code>toLowerCase</code> 不会影响字符串本身的值。</p>

<h2 id="示例">示例</h2>

<h3 id="例子：使用_toLowerCase">例子：使用 <code>toLowerCase()</code></h3>

<pre class="brush: js">console.log('中文简体 zh-CN || zh-Hans'.toLowerCase());
// 中文简体 zh-cn || zh-hans

​console.log( "ALPHABET".toLowerCase() );
// "alphabet"</pre>

<div class="line-number"></div>

<p><strong>说明</strong></p>



<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-15.5.4.16', 'String.prototype.toLowerCase')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-string.prototype.tolowercase', 'String.prototype.toLowerCase')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-string.prototype.tolowercase', 'String.prototype.toLowerCase')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td> <br>
     </td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div>{{CompatibilityTable}}</div>

<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="相关链接">相关链接</h2>

<ul>
 <li>{{jsxref("String.prototype.toLocaleLowerCase()")}}</li>
 <li>{{jsxref("String.prototype.toLocaleUpperCase()")}}</li>
 <li>{{jsxref("String.prototype.toUpperCase()")}}</li>
</ul>