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JS MythBusters – An optimization handbook from a high level point of view

mythbusters.js.org

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Re: JS MythBusters – An optimization handbook from a high level point of view

#11

Post by mcphage »

glitcher wrote: post #3

> from a high level point of view Many of the examples I looked at were very granular and specific, but didn't have much explanation. Does high level point of view really mean brief and without elaboration? From a high level on JS optimization I would like to see more emphasis on which considerations are most likely to have the biggest impact on my code. Throwing everything in together as if they were all equal seems…

That was my take, too. It says "from a high level point of view", but the very first optimization was about using the != operator vs the >= operator in certain conditionals. I'm struggling to think of anything more low-level than that, in JS.

Re: JS MythBusters – An optimization handbook from a high level point of view

#12

Post by extrapickles »

TheAceOfHearts wrote: post #5

How many of these optimizations are just limited to V8? I swear I've heard somewhere that the try/catch limitation is specific to V8, and that other engines don't have that problem. Am I mistaken? EDIT: Also, this page is very difficult to read. I have a laptop with a great screen and the lack of contrast is annoying.

The styling definitely needs more contrast. The comments on the code examples are nearly impossible for me to read without highlighting them. Looking at the styling, comments are set to rgb(51,51,51) which is nowhere near enough contrast between the black background.

Re: JS MythBusters – An optimization handbook from a high level point of view

#13

Post by gsnedders »

hiteshk_msft wrote: post #6

Some of these suggestions are good but some caveats: - Lookup tables- while lookup tables are great, engines might sometimes convert switch statements to lookup tables too- Chakra does this when it's advantageous to do so - Try-catch- this seems like v8 specific advice. Chakra definitely does optimize functions with try-catch in it, and I think SpiderMonkey does too - Freeing memory- setting the reference to null doe…

> Try-catch- this seems like v8 specific advice.

Carakan doesn't either. But given that nowadays affects some old TVs (but still newish, I doubt most people replace TVs that often…) and Opera Mini's limited JS support… Yeah, okay, that doesn't matter. :)

Re: JS MythBusters – An optimization handbook from a high level point of view

#14

Post by Twirrim »

One of the defining thing about MythBusters was that they'd take a myth, build an experiment with at least some notion of control, and then carry it out, so you can actually see the results.

Instead this site seems to be "regurgitate myths". e.g. http://mythbusters.js.org/workflow/boolean-conditions.html

"Avoid using >= and <= unless necessary. It’s faster to use a simpler comparison." There's a trivial code example, and then absolutely no evidence to support the claim. No benchmarks, nothing.

Re: JS MythBusters – An optimization handbook from a high level point of view

#15

Post by mikeash »

TAForObvReasons wrote: post #9
hiteshk_msft wrote: post #6

Some of these suggestions are good but some caveats: - Lookup tables- while lookup tables are great, engines might sometimes convert switch statements to lookup tables too- Chakra does this when it's advantageous to do so - Try-catch- this seems like v8 specific advice. Chakra definitely does optimize functions with try-catch in it, and I think SpiderMonkey does too - Freeing memory- setting the reference to null doe…

> Try-catch- this seems like v8 specific advice. Chakra definitely does optimize functions with try-catch in it, and I think SpiderMonkey does too http://gs.statcounter.com/ certainly suggests that specifically optimizing for Chrome/V8 will benefit the majority of users (58% not including mobile, 50% including mobile). As with all statistics, take with a grain of salt.

Also keep in mind that 50% of users as a whole may not equate to 50% of your users.

Re: JS MythBusters – An optimization handbook from a high level point of view

#17

Post by mintplant »

hiteshk_msft wrote: post #6

Some of these suggestions are good but some caveats: - Lookup tables- while lookup tables are great, engines might sometimes convert switch statements to lookup tables too- Chakra does this when it's advantageous to do so - Try-catch- this seems like v8 specific advice. Chakra definitely does optimize functions with try-catch in it, and I think SpiderMonkey does too - Freeing memory- setting the reference to null doe…

> Lookup tables

This one also seems a bit iffy to me, depending on the stage of compilation, how often this code runs, how much information the engine is able to collect, and the size of your table. The initial unoptimized property lookups will likely be slower than if/else statements, and the engine may end up optimizing them with inline caches, which are essentially a chain of if/else comparisons and jumps between dynamically generated code stubs.

> Try-catch

Yep, SpiderMonkey does optimize this case.

Re: JS MythBusters – An optimization handbook from a high level point of view

#18

Post by mintplant »

Twirrim wrote: post #14

One of the defining thing about MythBusters was that they'd take a myth, build an experiment with at least some notion of control, and then carry it out, so you can actually see the results. Instead this site seems to be "regurgitate myths". e.g. http://mythbusters.js.org/workflow/boolean-conditions.html "Avoid using >= and <= unless necessary. It’s faster to use a simpler comparison." There's a trivial code example,…

I'm extremely skeptical of that claim, too. As far as I can tell SpiderMonkey for example will emit practically exactly the same code for >= and They also recommend using `let` and `const` over `var` for performance reasons in the "Scope" section, but I have to ask whether they benchmarked that at all. Engines may grow to take advantage of these signals over time for further optimization, but at the moment many ES6 features incur a performance penalty just because the code behind them is less mature. I don't know specifically about `let`/`const` but I'd be pleasantly surprised to learn that they boost performance anywhere yet.

[0] https://dxr.mozilla.org/mozilla-central/source/js/src/jit/Io...

Re: JS MythBusters – An optimization handbook from a high level point of view

#19

Post by et-al »

colemannerd wrote: post #4

I think this is not well researched enough. There doesn't appear to be any thought put into optimization vs. readability, and when the optimization improves enough speed to justify the poor readability.

This has been one of my biggest issues when people write illegible but supposedly lightning quick code. The biggest bottle-neck in software isn't language quirks, but the person reading your code when it breaks.

Also, when Google or whoever decides to update the engine and compiles things differently, these hacks might become less efficient than just following best practices.

Re: JS MythBusters – An optimization handbook from a high level point of view

#20

Post by choward »

Twirrim wrote: post #14

One of the defining thing about MythBusters was that they'd take a myth, build an experiment with at least some notion of control, and then carry it out, so you can actually see the results. Instead this site seems to be "regurgitate myths". e.g. http://mythbusters.js.org/workflow/boolean-conditions.html "Avoid using >= and <= unless necessary. It’s faster to use a simpler comparison." There's a trivial code example,…

Exactly. There are no myths. There is no mythbusting. This has absolutely nothing to do with mythbusters.

It's just some random opinions about optimizations you most likely don't need. Who cares if something is barely faster? If the slower way is a lot more readable, I'm opting for that.

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