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| author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
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| committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
| commit | 33058f2b292b3a581333bdfb21b8f671898c5060 (patch) | |
| tree | 51c3e392513ec574331b2d3f85c394445ea803c6 /files/zh-cn/web/javascript/reference/statements/empty/index.html | |
| parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
| download | translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.tar.gz translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.tar.bz2 translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.zip | |
initial commit
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diff --git a/files/zh-cn/web/javascript/reference/statements/empty/index.html b/files/zh-cn/web/javascript/reference/statements/empty/index.html new file mode 100644 index 0000000000..3a03a63165 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/statements/empty/index.html @@ -0,0 +1,103 @@ +--- +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 < 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> |
