mapObject - 배열 -> map

const mapObject = (arr, fn) =>
  (a => (
    (a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
  ))();

 

const squareIt = arr => mapObject(arr, a => a * a);

squareIt([1, 2, 3]);    // { 1: 1, 2: 4, 3: 9 }