Message from JavaScript talks

July 2017

— This gets invoked inside a damn medusa snake head function lol

—

for (let i = 0; i < arr.length; i++) {
}

is slower than

const arrLength = arr.length;
for (let i = 0; i < arrLength; i++) {
}

— Really?

— Yep

— How did you find that out?

— Because .length runs some code to calculate the length when you access it

— All I read said it was just as fast

— This is the opposite of what I thought it did

— As far as I could tell it is efficient on normal arrays

— Https://stackoverflow.com/questions/17989270/for-loop-performance-storing-array-length-in-a-variable

— So I guess V8 is smart enough to optimize it nowadays

— Hm, but the dereference, is it that substantial?