minBy

1/**
2 * Returns the item with the minimum value based on a selector function.
3 *
4 * @param arr - Array of items.
5 * @param fn - Function that returns a numeric value from each item.
6 * @returns The item with the smallest selected value, or undefined if empty.
7 */
8export function minBy<T>(arr: T[], fn: (item: T) => number): T | undefined {
9  if (arr.length === 0) return undefined;
10
11  return arr.reduce((min, curr) =>
12    fn(curr) < fn(min) ? curr : min
13  );
14}

1test('minBy - basic usage', () => {
2  const data = [{ x: 3 }, { x: 1 }, { x: 4 }];
3  expect(minBy(data, item => item.x)).toEqual({ x: 1 });
4});
5
6test('minBy - same values', () => {
7  const data = [{ x: 2 }, { x: 2 }];
8  expect(minBy(data, item => item.x)).toEqual({ x: 2 });
9});
10
11test('minBy - negative numbers', () => {
12  const data = [{ n: -5 }, { n: 0 }, { n: 2 }];
13  expect(minBy(data, item => item.n)).toEqual({ n: -5 });
14});
15
16test('minBy - empty array', () => {
17  expect(minBy([], x => 1)).toBeUndefined();
18});