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    <p>Yes, what you have there is right. Some notes:</p> <ul> <li><code>bar</code> is created on every call to the function <code>foo</code>, but: <ul> <li>On modern browsers this is a very fast process. (Some engines may well only compile the <em>code</em> for it once, and then reuse that code with a different context each time; Google's V8 engine [in Chrome and elsewhere] does that in most cases.)</li> <li>And depending on what <code>bar</code> does, some engines may determine that they can "inline" it, eliminating the function call entirely. V8 does this, and I'm sure it's not the only engine that does. Naturally they can only do this if it doesn't change the behavior of the code.</li> </ul></li> <li>The performance impact, if any, of having <code>bar</code> created every time will vary widely between JavaScript engines. If <code>bar</code> is trivial, it will vary from undetectable to fairly small. If you're not calling <code>foo</code> thousands of times in a row (for instance, from a <code>mousemove</code> handler), I wouldn't worry about it. Even if you are, I'd only worry about it if I saw a problem on slower engines. <a href="http://jsperf.com/cost-of-creating-inner-function-v2" rel="nofollow noreferrer">Here's a test case involving DOM operations</a>, which suggests that there is an impact, but a trivial one (probably washed out by the DOM stuff). <a href="http://jsperf.com/cost-of-creating-inner-function/3" rel="nofollow noreferrer">Here's a test case doing pure computation</a> which shows a much higher impact, but frankly even, we're talking a difference of <em>micro</em>seconds because even a 92% increase on something that takes <em>micro</em>seconds to happen is still very, very fast. Until/unless you saw a real-world impact, it's not something to worry about.</li> <li><code>bar</code> will only be accessible from within the function, and it has access to all variables and arguments for that call to the function. This makes this a very handy pattern.</li> <li>Note that because you've used a function <em>declaration</em>, it doesn't matter where you put the declaration (top, bottom, or middle&nbsp;&mdash; as long as it's at the top level of the function, not inside a flow control statement, which is a syntax error), it gets defined before the first line of step-wise code is run.</li> </ul>
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    1. COThx for your answer. So are you saying that this is a negligible performance hit? (given that a copy of `bar` is created on every call of `foo`)
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    2. CO@ahmoo: With JavaScript performance, the answer is almost always: It depends. :-) It depends on what engine will be running it and how frequently you'll be calling `foo`. If you're not calling `foo` thousands of times in a row (for instance, not in a `mousemove` handler), then I wouldn't be worried about it at all. And note that some engines (V8, for instance) will inline the code anyway, completely eliminating the function call, provided doing so doesn't change what's happening in a way that can be detected externally.
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    3. COThanks. You have got some great points.
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