mapObject

Maps the values of an array to an object using a function.

• Use Array.prototype.reduce() to apply fn to each element in arr and combine the results into an object.
• Use el as the key for each property and the result of fn as the value.

const mapObject = (arr, fn) =>
  arr.reduce((acc, el, i) => {
    acc[el] = fn(el, i, arr);
    return acc;
  }, {});

mapObject([1, 2, 3], a => a * a); // { 1: 1, 2: 4, 3: 9 }