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Discussion on: Write a Custom JavaScript Filter Function that is 60% faster than Array.filter

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Functional Javascript Author

Interesting, using your example I get massive speed boost on both mac and windows using the loop.
To test properly, run each independently to avoid compiler optimizations of one influencing the other.

Yes a microoptimization would be small changes, like 5 to 10%.
But when it's running many times faster, you want to use the most perfomant.

There is nothing special about the built-in functions that the compiler will optimize better than custom functions. Though some of it may run in C++, it all runs in the V8 sandbox.
In rare cases the V8 team will optimize the V8 engine for some operations on new releases, usually on major releases.

In almost all cases a simple loop will always win out.

However many algorithms will vary in performance due to the data profile.

When you have a set of tools that can test a function you've written in less than a minute, it's worth it.
It's not always about comparing with the built-in function, though you should add them to the set of candidate algorithms if apropos.

Readability is not related to the complexity of the function.
The documentation is.
For example, you're not going to choose not to use memoization just because it's more readable not to, when it could improve the performance of your code 10x or 100x.

By testing the performance of your functions, means you understand your functions better; you understand the compiler better; you understand what idioms work better, and you make your codebase more performant as a whole.

I agree with you that everything has pros and cons that must be evaluated. And that I wouldn't worry about the small differences, and focus on the big difference.
But you should performance test all your functions, and robust test them, and fuzz test them.

Thanks for your input and testing that out. Your input is valuable!

const lt = console.time;
const le = console.timeEnd;

const a = genNums(10e6);
// const a = genRandNums(1, 10e6, 10e6);

// fil: 73.986ms - on windows
// fil: 33.733ms - mac
fil(n => n < 8, a);

// filter: 506.438ms - on windows
// filter: 153.095ms - on mac
a.filter(n => n < 8);


I have a post here on how to evaluate what code to use before commiting it to production.

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