DEV Community

6 times faster loops in Javascript

Eckehard on March 19, 2024

Javascript is fast. Really fast - at least if it´s running in a modern browser. So, in general you should not care too much about performance. But ...

Read full post

KooiInc • Mar 19

Not sure how these results are obtained. Maybe you should also publish the code you used to test.

I Tried to reproduce using the information you gave us and with a few new approaches: see this snippet. The results are different.

Eckehard • Mar 19

Results will greatly depend on your machine and the browser. I added my test code at the end of the post so you can try the tests I did.

KooiInc • Mar 20 • Edited

Right, so you're telling us you tested a text with 4625 lines, but in the snippet you are testing a text with 251 lines - the result of which you use here.

Eckehard • Mar 20

Oh, sorry, my fault! 4625 was the file length, not the line count. I changed the text, thank you for the hint!

You will find that results will greatly change on different machines. On and Intel(R) Core(TM) i7-1185G7 for..of was the winner, but the speed factor was only 2.7 to the slowest result.

KooiInc • Mar 20

Ok, both cases are now covered in my snippet. And yes, it (ofcourse) also depends on the used hardware.

BTW I would advice to always use semicolons for line ends in EcmaScript.

Eckehard • Mar 20

I have done a lot coding in C and Pascal, but did not miss the semicolons for any reason. Beside of personal taste, is there any technical reason to use semicolons?

KooiInc • Mar 20

Most of the time it's not relevant. I've coded ~~Java/~~ECMAScript since its conception (besides pascal, c, c++ and c#). Still every now and then I run into a problem because of the interpreters' automatic semicolon insertion *). So I force myself to use them.

*) for example

function add(a, b) {
  return
    a + b
}
add(1,2); // undefined

Alex Lohr • Mar 19

Maybe

const lines = text.replace(/(\n|$)/g, "x$1")

Might be worth a try, too.

Eckehard • Mar 19

In my setup regEx-replace was about 20% slower than the slowest solution, which is still not bad. Things might change if the task get´s more complicated, but in general I found that regEx performance is quite reasonable, Not top of the list, but also not much slower than hand optimized code. If you take into account that RegEx expressions can be quite complex, this is still an amazing result.