Implement a function maxBy(array, iteratee) that finds the maximum element in an array based on the specified criteria.

The function should:

• Accept an array and an iteratee function.
• Apply the iteratee to each element to generate a criterion for comparison.
• Return the element that has the maximum criterion value.
• Return undefined if the array is empty.

Examples

maxBy([1, 2, 3, 4], x => x);                  // 4
maxBy([{ n: 1 }, { n: 2 }], o => o.n);        // { n: 2 }
maxBy(['apple', 'banana', 'kiwi'], s => s.length); // "banana"
maxBy([], x => x);                            // undefined