index.ts

export const VERSION = '1.4.0';

export function sleep(timeout: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, timeout));
}

export function queueFactory() {
  let queueImpl: Promise<unknown> = Promise.resolve();
  return <T,>(fx: () => Promise<T> | T): Promise<T> => {
    queueImpl = queueImpl.then(fx, fx);
    return queueImpl as Promise<T>;
  };
}

export function throttlingQueueFactory({ delay }: { delay: number }) {
  let queueImpl = queueFactory();
  return (fx: () => unknown): Promise<unknown> => {
    const res = queueImpl(fx);
    queueImpl(() => sleep(delay));
    return res;
  };
}

export function singleInstance<T extends (...args: any[]) => Promise<unknown>>(fx: T) {
  let instance: ReturnType<T> | null = null;
  return (...args: Parameters<T>): ReturnType<T> => {
    if (!instance) {
      instance = fx(...args) as ReturnType<T>;
      instance.then(() => instance = null, () => instance = null);
    }
    return instance;
  };
}