Max array value based on function

Returns the maximum value of an array, after mapping each element to a value using the provided function.

• Use Array.prototype.map() to map each element to the value returned by fn.
• Use Math.max() to get the maximum value.

const maxBy = (arr, fn) =>
  Math.max(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));

maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], x => x.n); // 8
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 8