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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/operators/comma_operator | |
| parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
| download | translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.tar.gz translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.tar.bz2 translated-content-33058f2b292b3a581333bdfb21b8f671898c5060.zip | |
initial commit
Diffstat (limited to 'files/zh-cn/web/javascript/reference/operators/comma_operator')
| -rw-r--r-- | files/zh-cn/web/javascript/reference/operators/comma_operator/index.html | 84 |
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diff --git a/files/zh-cn/web/javascript/reference/operators/comma_operator/index.html b/files/zh-cn/web/javascript/reference/operators/comma_operator/index.html new file mode 100644 index 0000000000..0636731b0b --- /dev/null +++ b/files/zh-cn/web/javascript/reference/operators/comma_operator/index.html @@ -0,0 +1,84 @@ +--- +title: 逗号操作符 +slug: Web/JavaScript/Reference/Operators/Comma_Operator +tags: + - comma operator + - 逗号操作符 +translation_of: Web/JavaScript/Reference/Operators/Comma_Operator +--- +<div> +<div>{{jsSidebar("Operators")}}</div> +</div> + +<p><strong>逗号操作符 </strong> 对它的每个操作数求值(从左到右),并返回最后一个操作数的值。</p> + +<p>{{EmbedInteractiveExample("pages/js/expressions-commaoperators.html")}}</p> + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox"><em>expr1</em>, <em>expr2, expr3...</em></pre> + +<h2 id="参数">参数</h2> + +<dl> + <dt><code>expr1</code>, <code>expr2, expr3...</code></dt> + <dd>任一表达式。</dd> +</dl> + +<h2 id="描述">描述</h2> + +<p>当你想要在期望一个表达式的位置包含多个表达式时,可以使用逗号操作符。这个操作符最常用的一种情况是:<code>for</code> 循环中提供多个参数。</p> + +<h2 id="示例">示例</h2> + +<p>假设 <code>a</code> 是一个二维数组,每一维度包含10个元素,则下面的代码使用逗号操作符一次递增/递减两个变量。需要注意的是,<code>var</code> 语句中的逗号<em><strong>不是</strong></em>逗号操作符,因为它不是存在于一个表达式中。尽管从实际效果来看,那个逗号同逗号运算符的表现很相似。但确切地说,它是 <code style="font-style: normal;">var</code> 语句中的一个特殊符号,用于把多个变量声明结合成一个。下面的代码打印一个二维数组中斜线方向的元素:</p> + +<pre class="brush:js;highlight:[1]">for (var i = 0, j = 9; i <= 9; i++, j--) + document.writeln("a[" + i + "][" + j + "] = " + a[i][j]);</pre> + +<h3 id="处理后返回">处理后返回</h3> + +<p>另一个使用逗号操作符的例子是在返回值前处理一些操作。如同下面的代码,只有最后一个表达式被返回,其他的都只是被求值。</p> + +<pre>function myFunc () { + var x = 0; + + return (x += 1, x); // the same of return ++x; +}</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>ECMAScript 1st Edition.</td> + <td>Standard</td> + <td>Initial definition.</td> + </tr> + <tr> + <td>{{SpecName('ES5.1', '#sec-11.14', 'Comma operator')}}</td> + <td>{{Spec2('ES5.1')}}</td> + <td> </td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-comma-operator', 'Comma operator')}}</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>{{Compat("javascript.operators.comma")}}</p> + +<h2 id="See_also" name="See_also">参见</h2> + +<ul> + <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for">for loop</a></li> +</ul> |
