Javascript Array newMap(fn)

Array.prototype.newMap = function (fn) {
 let result = []/*w  w w .  j ava  2  s . c om*/

 this.reduce((a, b, i) => {
  result.push(fn.call(this, a, i - 1, this));

  if (i + 1 === this.length) {
   result.push(fn.call(this, b, i, this));
  }

  return b;
 })

 return result;
}

let arr = [1,2,3,4,5];

console.log(arr.newMap((item, index, arr) => {
 console.log(item, index, arr);
 return item + 1;
}));