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authorPeter Bengtsson <mail@peterbe.com>2020-12-08 14:40:17 -0500
committerPeter Bengtsson <mail@peterbe.com>2020-12-08 14:40:17 -0500
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+---
+title: empty
+slug: Web/JavaScript/Reference/Statements/Empty
+tags:
+ - JavaScript
+ - Statement
+translation_of: Web/JavaScript/Reference/Statements/Empty
+---
+<div>
+<div>{{jsSidebar("Statements")}}</div>
+</div>
+
+<p><strong>空语句</strong>用来表明没有语句,尽管 JavaScript 语法希望有语句。</p>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox">;
+</pre>
+
+<h2 id="描述">描述</h2>
+
+<p><span class="short_text" id="result_box" lang="zh-CN"><span>空语句是一个分号(;),表示不会执行任何语句,即使 JavaScript 语法需要一个语句。</span></span> 相反,当你需要多行语句,但 JavaScript 只允许一个时,可以使用<a href="/zh-CN/docs/Web/JavaScript/Reference/Statements/block">语句块</a>;语句块可以将多条语句合并为一个。</p>
+
+<h2 id="示例">示例</h2>
+
+<p>空<span class="short_text" lang="zh-CN"><span>语句有时与循环语句一起使用。以下示例使用空循环体:</span></span></p>
+
+<pre class="brush: js">var arr = [1, 2, 3];
+
+// Assign all array values to 0
+for (let i = 0; i &lt; arr.length; arr[i++] = 0) /* empty statement */ ;
+
+console.log(arr)
+// [0, 0, 0]
+</pre>
+
+<p><strong>提示:</strong>在使用空语句的情况下专门写上注释是个不错的主意,因为不是很容易区分空语句和普通的分号。下面的示例可能不是故意加上分号的:</p>
+
+<pre class="brush: js">if (condition); // Caution, this "if" does nothing!
+ killTheUniverse() // So this gets always executed!!!
+</pre>
+
+<p>另一个例子:<a href="/en-US/docs/Web/JavaScript/Reference/Statements/if...else"><code>if...else</code></a> 语句不带花括号(<code>{}</code>)。如果<code>three</code>为<code>true</code>, 不会发生任何事,<code>four</code>不会执行,同时<code>else</code>从句中的<code>launchRocket()</code>函数也不会执行。</p>
+
+<pre class="brush: js">if (one)
+ doOne();
+else if (two)
+ doTwo();
+else if (three)
+ ; // nothing here
+else if (four)
+ doFour();
+else
+ launchRocket();</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('ESDraft', '#sec-empty-statement', 'Empty statement')}}</td>
+ <td>{{Spec2('ESDraft')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES6', '#sec-empty-statement', 'Empty statement')}}</td>
+ <td>{{Spec2('ES6')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES5.1', '#sec-12.3', 'Empty statement')}}</td>
+ <td>{{Spec2('ES5.1')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES3', '#sec-12.3', 'Empty statement')}}</td>
+ <td>{{Spec2('ES3')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES1', '#sec-12.3', 'Empty statement')}}</td>
+ <td>{{Spec2('ES1')}}</td>
+ <td>Initial definition.</td>
+ </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容">浏览器兼容</h2>
+
+
+
+<p>{{Compat("javascript.statements.empty")}}</p>
+
+<h2 id="See_also" name="See_also">相关链接</h2>
+
+<ul>
+ <li>{{jsxref("Statements/block", "块语句")}}</li>
+</ul>