useIdleMapReduce

useIdleMapReduce.ts

function useIdleMapReduce<T = any, M = T, R = M>(
  array: T[],
  map: (item: T, index: number, array: T[]) => M,
  reduce: (acc: R, value: M, index: number, array: M[]) => R,
  initialValue: R
) {
  const ref = useRef({ array, out: [] as M[], acc: initialValue, index: 0, id: null });
  const result = useCallback(() => {
    if (ref.current.index !== -1) callback(true);
    return ref.current.acc;
  }, [ref, array]);

  const schedule = (fn: () => void) => {
    ref.current.id = window.requestIdleCallback(() => fn());
  };

  const callback = (finish?: boolean) => {
    const now = Date.now();

    const { array: a, out } = ref.current;
    while (ref.current.index < a.length) {
      out[ref.current.index] = map(a[ref.current.index], ref.current.index, a);
      ref.current.acc = reduce(ref.current.acc, out[ref.current.index], ref.current.index, out);
      ref.current.index = ref.current.index + 1;

      if (!finish && Date.now() - now > 62 && ref.current.index < a.length) {
        schedule(callback);
        return;
      }
    }

    ref.current.index = -1;
    ref.current.id = null;
  };

  useMemo(() => {
    if (ref.current.array !== array) {
      if (ref.current.id) window.cancelIdleCallback(ref.current.id);

      ref.current.array = array;
      ref.current.out = [];
      ref.current.index = 0;
      ref.current.id = null;
      ref.current.acc = initialValue;
    }

    if (Array.isArray(array) && !ref.current.id) {
      schedule(callback);
    }
  }, [array]);

  return result;
}