Run results for: for vs for...in vs for...of vs forEach

Run details:

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:121.0) Gecko/20100101 Firefox/121.0

Browser: Firefox 121

Operating system: Linux

Device Platform: Desktop

Date tested: 2 years ago

for...in

63.1M/s

forEach

15.2M/s

for

2K/s

for...of

2K/s

View exact numbers

Test name	Executions per second
✓ for...in	63,142,388 Ops/sec
forEach	15,152,928 Ops/sec
for	1,942 Ops/sec
for...of	1,902 Ops/sec

Script Preparation code:

function randNum(max, min) {
	const x = Math.floor(Math.random() * max)
	if (!isFinite(min) && x < min) {
		return min
	}
	return x
}

function randString(max, min, base) {
	let len = randNum(max)
	if (min && len < min) {len = min}
	if (len > max) {len = max}

	let arr = new Uint8Array(len / 2)
	window.crypto.getRandomValues(arr)
	return Array.from(arr, (dec)=> (
		dec.toString(base || 36).padStart(2, '0')
	)).join('')
}

var list = Object.freeze(
	Array(100).map(()=> Object.freeze({
		id: randString(64,64),
		firstName: randString(40,5),
		lastName: randString(40,5),
		email: randString(40,5),
		address: Object.freeze({
			country: randString(40,5),
			state: randString(40,5),
		}),
	}))
)

Tests:

for
for (let i = 0; i < list.length; i++) {const el = list[i]; console.count('for')}
for...in
for (const elIdx in list) {const el = list[elIdx]; console.count('for...in')}
for...of
for (const el of list) {console.count('for...of')}
forEach
list.forEach((el)=> console.count('forEach'))

Run results for: for vs for...in vs for...of vs forEach

Benchmarks the speed of different iteration implementations

for

for...in

for...of

forEach