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In JavaScript, I've an object with an array, and a method wich gets a slice of that array and a concatenation with another array.

If that method is run several times in the same function to return always the same value, does the performance will be faster after of the first run (due to the result will be cached in CPU cache)?

  • You might have to provide a little bit more explanation or example of the code in question. The slightly-short answer however is that it is implementation specific to the javascript parser that is executing the code. The short answer is no. – Quintin Robinson Oct 30 '12 at 19:57
  • `processor cache` is awfully low-level to inspect. I'd say *you never know*. There could be so many other things running, which might find a place in cache, that the JS Parser's instructions might/might not get a place in the instruction caches. It is certainly not something to count on. – Anirudh Ramanathan Oct 30 '12 at 19:59

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Of course no is the only answer would be here. Because the purpose of a function is to take some parameters and return a value. All the parameters might be different each time you call the function and even if they are the same, the result might be different, also event if you call the function and each time it returns the same result, because it might do an action or cause some modifications in other places, caching the result by the parser would be a buggy idea.

Cheers

Rikki
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I guess the general answer to this question is NO! There is no caching in JavaScript or CPU caching that you can control with JavaScript. If you need to cache something / increase performance, i will have to program that yourself.

See this small example: http://jsperf.com/cachingjq

Tys
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    The processor could cache the instructions the JS parser generated. How are you so sure it doesn't? CPU caches aren't in the user's control. – Anirudh Ramanathan Oct 30 '12 at 20:02
  • That's what i mean; there is nothing you can control with your JavaScript code. (As far as i know). Of course different Javascript engines or CPU could do something specific, but it's not that you can say, when i write code like this, i'm taking advantage of CPU caching. – Tys Oct 30 '12 at 21:14
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Maybe.

There are quite a lot of levels of cache to look at, here. Your processor alone has more than a single cache. Basically, though, you simply can't say much about those. They might have different sizes, things like what other things you do in the mean time and how long the function is all influence this. It should also be noted that this does not work at the level of what you call a function call when in Javascript, but at a much lower level. However, it might at times mean that some time can be shaved off of the execution time of the function. I don't think it's too likely or noticeable, but in the end, you can't really say much about it.

Finally, there is javascript itself. Per the standard, it doesn't have such caching. However, the standard doesn't prohibit strange caching either, so there might one day be a browser that does it like that (I don't believe there is one right now.)

In the end, the basic answer is: no not in a noticeable way. However, there might actually be a speed gain due to the cache, it's always hard to say.

Jasper
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No, you'd have to manually (or with a framework) memoize the results: Javascript Memoization Explanation?

Community
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Dexygen
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