Improving on the bad map

bettermap.es

// See https://gist.github.com/liorean/58667acd9b8b4554a9c7b4740065e93c

const map=(f,array)=>{
  const iterator=array[Symbol.iterator]()
  let {done,value}=iterator.next()
  if(done){
    if('return' in iterator)
      iterator.return()
    return []}
  return [f(value),...map(f,iterator)]}

console.log(map(e=>2**e,[0,1,2,3,4,5,6,7,8,9]))

//> ch bettermap.es
//  1,2,4,8,16,32,64,128,256,512
//> js bettermap.es
//  1,2,4,8,16,32,64,128,256,512
//> node bettermap.es
//  [ 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 ]