Tail resursion in JS

tail-recursion.js

// the non-tail-recursive way
;(() => {
  function fac(n) {
    if (n === 1) {
      return 1
    }
    const nextFac = fac(n - 1)
    return n * nextFac // last thing we do it multiply
  }

  const start = Date.now()
  console.log(`factorial of 5=${fac(5)}`)
  console.log(`factorial of 24=${fac(24)}`)
  console.log(Date.now() - start)
})()

// tail-recursive
;(() => {
  function fac(n) {
    if (n === 1) {
      return 1
    }
    return go(n, n - 1)
  }

  function go(accum, n) {
    const newAccum = accum * n
    if (n === 1) {
      return newAccum
    }
    return go(newAccum, n - 1) // last thing we do is recurse
  }

  const start = Date.now()
  console.log(`factorial of 5=${fac(5)}`)
  console.log(`factorial of 24=${fac(24)}`)
  console.log(Date.now() - start)
})()