mapKeys

Maps the keys of an object using the provided function, generating a new object.

• Use Object.keys() to iterate over the object's keys.
• Use Array.prototype.reduce() to create a new object with the same values and mapped keys using fn.

const mapKeys = (obj, fn) =>
  Object.keys(obj).reduce((acc, k) => {
    acc[fn(obj[k], k, obj)] = obj[k];
    return acc;
  }, {});

mapKeys({ a: 1, b: 2 }, (val, key) => key + val); // { a1: 1, b2: 2 }