Design Meeting Notes, 6/18/2024 about typescript

[Jamesernator]

I'd have expected for (const foo of foos) {} to be highly optimized by engines at this point. Since the iterator for arrays doesn't actually do anything, I'd be surprised if most engines didn't optimize it away in this case.

Still not really, a for-of-loop is still often many times slower than a for-loop, e.g. this has a difference of 10x in v8 , and 4x in jsc (curiously inlining the forOfLoop function makes v8 have a 4x difference as well):

const arr = Array.from({ length: 10_000_000 }, () => Math.random());

function forLoop() {
    let sum = 0;
    for (let i = 0; i < arr.length; i += 1) {
        sum += arr[i];
    }
}

function forOfLoop() {
    let sum = 0;
    for (const v of arr) {
        sum += v;
    }
}

console.time("for-loop");
for (let i = 0; i < 100; i += 1) {
    forLoop();
}
console.timeEnd("for-loop");

console.time("for-of-loop");
for (let i = 0; i < 100; i += 1) {
    forOfLoop();
}
console.timeEnd("for-of-loop");

[fatcerberus]

for-of loops create iterators but for (let i = 0; i < arr.length; i++) doesn't.

I'd have expected for (const foo of foos) {} to be highly optimized by engines at this point. Since the iterator for arrays doesn't actually do anything, I'd be surprised if most engines didn't optimize it away in this case.