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75 lines
2.2 KiB
XML
75 lines
2.2 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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Non-standard language extensions such as expression closures or <code>let</code> expressions should
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be avoided, since they make code harder to read or reuse.
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</p>
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</overview>
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<recommendation>
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<p>
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Use standard language features instead. For instance, expression closures can be
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replaced by ECMAScript 2015 arrow functions, or alternatively by plain functions;
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<code>let</code> statements and expressions can be replaced by ECMAScript 2015
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<code>let</code> declarations; and <code>for each ... in</code> statements
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can be replaced by ECMAScript 2015 <code>for ... of</code> statements.
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</p>
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</recommendation>
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<example>
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<p>
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The following example uses an expression closure with <code>map</code>:
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</p>
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<sample src="examples/ExpressionClosures.js" />
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<p>
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The equivalent code using an ECMAScript 2015 arrow function is as follows:
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</p>
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<sample src="examples/ExpressionClosuresGood.js" />
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<p>
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On ECMAScript 2015 platforms, a plain function can be used instead:
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</p>
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<sample src="examples/ExpressionClosuresGood2.js" />
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<p>
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As another example, consider this use of a <code>let</code> statement:
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</p>
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<sample src="examples/LetStatement.js"/>
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<p>
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It can easily be replaced by a block-scoped <code>let</code> declaration:
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</p>
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<sample src="examples/LetStatementGood.js"/>
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<p>
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Older versions of Firefox support a postfix notation for array comprehensions:
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</p>
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<sample src="examples/PostfixComprehension.js"/>
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<p>
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This notation should be converted into the semantically equivalent prefix notation
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supported by newer browsers:
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</p>
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<sample src="examples/PostfixComprehensionGood.js"/>
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</example>
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<references>
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<li>Mozilla Developer Network: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions">Arrow functions</a>.</li>
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<li>Mozilla Developer Network: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#Non-standard_let_extensions">Non-standard let extensions</a>.</li>
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<li>Mozilla Developer Network: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for_each...in">for each...in</a>.</li>
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</references>
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</qhelp>
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