intersection

1/**
2 * Returns a new array containing elements that exist in both input arrays.
3 * Preserves order from the first array.
4 * Supports primitive values by default.
5 *
6 * @param a - The first array.
7 * @param b - The second array.
8 * @returns A new array with shared elements between 'a' and 'b'.
9 */
10export function intersection<T>(a: T[], b: T[]): T[] {
11  const setB = new Set(b);
12  return a.filter(item => setB.has(item));
13}

1test('intersection with shared elements', () => {
2  expect(intersection([1, 2, 3], [2, 3, 4])).toEqual([2, 3]);
3});
4
5test('intersection with no common elements', () => {
6  expect(intersection([1, 2], [3, 4])).toEqual([]);
7});
8
9test('intersection with duplicates in input', () => {
10  expect(intersection([1, 2, 2, 3], [2, 3])).toEqual([2, 2, 3]);
11});
12
13test('intersection with empty second array', () => {
14  expect(intersection([1, 2, 3], [])).toEqual([]);
15});
16
17test('intersection with empty first array', () => {
18  expect(intersection([], [1, 2, 3])).toEqual([]);
19});
20
21test('intersection with different types', () => {
22  expect(intersection(['a', 'b'], ['b', 'c'])).toEqual(['b']);
23});