Min and max of array based on provided function

JavaScript, Array · Nov 3, 2020

Returns the minimum/maximum value of an array, after applying the provided function to set the comparing rule.

Use Array.prototype.reduce() in combination with the comparator function to get the appropriate element in the array.
Omit the second argument, comparator, to use the default one that returns the minimum element in the array.

const reduceWhich = (arr, comparator = (a, b) => a - b) =>
  arr.reduce((a, b) => (comparator(a, b) >= 0 ? b : a));

reduceWhich([1, 3, 2]); // 1
reduceWhich([1, 3, 2], (a, b) => b - a); // 3
reduceWhich(
  [
    { name: 'Tom', age: 12 },
    { name: 'Jack', age: 18 },
    { name: 'Lucy', age: 9 }
  ],
  (a, b) => a.age - b.age
); // {name: 'Lucy', age: 9}