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113 lines
9.0 KiB
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<article id="wikiArticle">
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<div></div>
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<p>圆括号运算符<code>( )</code> 用来控制表达式中的运算优先级。</p>
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<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/expressions-groupingoperator.html" width="100%"></iframe></div>
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<p class="hidden">这些交互的事例资源都是基于Github的仓库.如果你想提交更多的交互事例,请克隆这个url<a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> 并且向我们发送合并请求</p>
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<h2 id="语法">语法</h2>
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<pre class="syntaxbox"> ( )</pre>
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<h2 id="说明">说明</h2>
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<p>圆括号运算符由一对圆括号组成,包裹表达式和子表达式用来覆盖常规的 <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence">运算符优先级</a> ,达到低优先级的表达式比高优先级的表达式更早运算.</p>
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<h2 id="示例">示例</h2>
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<p>下面的代码展示了加法运算先于乘法运算的情况.</p>
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<pre class="brush:js">var a = 1;
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var b = 2;
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var c = 3;
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// default precedence
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a + b * c // 7
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// evaluated by default like this
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a + (b * c) // 7
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// now overriding precedence
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// addition before multiplication
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(a + b) * c // 9
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// which is equivalent to
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a * c + b * c // 9
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</pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</th>
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</tr>
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<tr>
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<td><a class="external" href="https://tc39.github.io/ecma262/#sec-grouping-operator" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">The Grouping Operator</small></a></td>
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<td><span class="spec-Draft">Draft</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-grouping-operator" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">The Grouping Operator</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-11.1.6" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">The Grouping Operator</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf#sec-11.1.4" hreflang="en" lang="en" rel="noopener">ECMAScript 1st Edition (ECMA-262)<br/><small lang="zh-CN">The Grouping Operator</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>初始化定义.在JavaScript1.0中生效</td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
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<div class="hidden">本页的浏览器兼容性表都是基于结构数据，如果你想更新数据.可以查看 <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> 并且请给我们发送合并请求.</div>
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<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row">Grouping operator <code>()</code></th><td class="bc-supports-yes bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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1</td><td class="bc-supports-yes bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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4</td><td class="bc-supports-yes bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
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<abbr class="bc-level bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr></span></dt><dd>Full support</dd></dl></section></div><p></p>
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<h2 id="See_also" name="See_also">相关链接</h2>
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<ul>
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<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence">运算符优先级</a></li>
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<li><a href="Reference/Operators/delete" title="delete 操作符用于删除对象的某个属性；如果没有指向这个属性的引用，那它最终会被释放。"><code>delete</code></a></li>
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<li><a href="Reference/Operators/typeof" title="typeof操作符返回一个字符串，表示未经计算的操作数的类型。"><code>typeof</code></a></li>
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</ul>
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</article> |