oncePerKey

1/**
2 * Creates a function that ensures the callback is only called once per unique key.
3 * Includes a .reset() method to clear the internal call tracking.
4 *
5 * @param fn - The function to call.
6 * @returns A function that takes a key and calls `fn` only once per unique key.
7 */
8export function oncePerKey<K = string>(
9  fn: (key: K) => void
10): ((key: K) => void) & { reset: () => void } {
11  const called = new Set<K>();
12
13  const wrapper = (key: K) => {
14    if (!called.has(key)) {
15      called.add(key);
16      fn(key);
17    }
18  };
19
20  wrapper.reset = () => {
21    called.clear();
22  };
23
24  return wrapper;
25}

1test('oncePerKey - calls function only once per key', () => {
2  const spy = jest.fn();
3  const once = oncePerKey(spy);
4
5  once('a');
6  once('a');
7  once('b');
8  once('b');
9
10  expect(spy).toHaveBeenCalledTimes(2);
11  expect(spy).toHaveBeenCalledWith('a');
12  expect(spy).toHaveBeenCalledWith('b');
13});
14
15test('oncePerKey - reset() allows keys to be reused', () => {
16  const spy = jest.fn();
17  const once = oncePerKey(spy);
18
19  once('x');
20  once('x');
21
22  once.reset();
23
24  once('x');
25  expect(spy).toHaveBeenCalledTimes(2);
26});
27
28test('oncePerKey - works with numbers as keys', () => {
29  const spy = jest.fn();
30  const once = oncePerKey<number>(spy);
31
32  once(1);
33  once(1);
34  once(2);
35  expect(spy).toHaveBeenCalledTimes(2);
36});