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49 lines
2.6 KiB
HTML
49 lines
2.6 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<h2 id="错误提示">错误提示</h2>
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<pre><code class="language-javascript">Warning: expression closures are deprecated
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</code></pre>
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<h2 id="错误类型">错误类型</h2>
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<p>警告。JavaScript 引擎不会停止运行。</p>
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<h2 id="哪里出错了？">哪里出错了？</h2>
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<p>非标准化的<a href="/en-US/docs/Web/JavaScript/Reference/Operators/Expression_closures">表达式闭包</a>语法（简写函数语法）已被废弃，不应该再被使用。该语法将会在 <a class="external" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1083458" rel="noopener" title="FIXED: Remove SpiderMonkey support for expression closures (shorthand function syntax)">bug 1083458</a> 中全部移除，到时候用到该语法的脚本程序会报 SyntaxError 错误。</p>
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<h2 id="示例">示例</h2>
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<h3 id="被废弃的语法">被废弃的语法</h3>
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<p>表达式闭包从函数声明或者对象方法定义中省略了花括号或是 return 语句。</p>
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<pre><code class="language-js example-bad">var x = function() 1;
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var obj = {
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count: function() 1
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};
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</code></pre>
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<h3 id="标准语法">标准语法</h3>
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<p>将非标准化的表达式闭包语法转换成标准 ECMAScript 语法，可以添加花括号以及 return 语句。</p>
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<pre><code class="language-js example-good">var x = function() { return 1; }
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var obj = {
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count: function() { return 1; }
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};
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</code></pre>
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<h3 id="标准语法之箭头函数">标准语法之箭头函数</h3>
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<p>另外，你可以选择使用箭头函数：</p>
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<pre><code class="language-js example-good">var x = () => 1;</code></pre>
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<h3 id="标准语法之方法的简略写法">标准语法之方法的简略写法</h3>
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<p>表达式闭包还会出现在 getter 与 setter 中，例如：</p>
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<pre><code class="language-js example-bad">var obj = {
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get x() 1,
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set x(v) this.v = v
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};
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</code></pre>
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<p>根据 ES2015 中对于<a href="/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions">方法定义</a>的规定，上述写法可以转换成如下形式：</p>
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<pre><code class="language-js example-good">var obj = {
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get x() { return 1 },
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set x(v) { this.v = v }
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};
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</code></pre>
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<h2 id="相关内容">相关内容</h2>
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<ul>
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<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Expression_closures">Expression closures</a></li>
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<li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions">Arrow functions</a></li>
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<li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions">Method definitions</a></li>
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</ul>
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</article> |