implementation of tail recursive and no tail recursive factorial

fac.js

function fac(n){
  if( n == 0) return 1
  return n * fac(n-1)
}

function fac2(n){
  return (function tmp( n , a){
    if(n == 0) return a 
    return tmp(n-1 , a * n)
  })(n , 1)
}