multiply-array-values-by-num.js

const recursiveMultiplier = (arr, num) => {
  let newArray = [];
  let mult = function(a) {
    if(a.length) {
      newArray[a.length-1] = a.pop()*num;
      mult(a);
      return newArray;
    }
    return;
  }
  return mult(arr);
}

let x = [1, 2, 3], num = 2;
let y = recursiveMultiplier(x,num);
console.log(y);