loop-time.js

const testLength = Number(process.argv[2] || 10000000)

console.log('Loop speed test')
console.log(`Initiating array with ${testLength} items`)

const arr = new Array(testLength).fill(1)

time(loopSimple)
time(loopForIn)
time(loopForOf)
time(forEach)
time(reduce)
time(loopSimple)
time(loopForIn)
time(loopForOf)
time(forEach)
time(reduce)

function time (f) {
  const start = Date.now()
  const value = f()
  const end = Date.now()
  if (value !== arr.length) throw new Error(`${f.name} does not work lols`)
  console.log(`${f.name} took ${end - start} ms`)
}

function loopSimple () {
  let res = 0
  for (let i = 0; i < arr.length; i++) res += arr[i]
  return res
}

function loopForIn () {
  let res = 0
  for (const i in arr) res += arr[i]
  return res
}

function loopForOf () {
  let res = 0
  for (const val of arr) res += val
  return res
}

function forEach () {
  let res = 0
  arr.forEach(val => res += val)
  return res
}

function reduce () {
  return arr.reduce((res, val) => res += val, 0)
}