promise-debounce.ts

export function debounce<F extends ((...args: any) => any)> (
  fn: F,
  ms: number
) {
  /**
   * Not the correct type, because of these conflicts:
   * - Node's setTimeout returns a `Timeout` object
   * - Browser's setTimeout returns a `number`
   * 
   * TypeScript doesn't provide an option to specifically exclude certain type
   * declarations, this is bothersome particularly in monorepo scenarios.
   * See microsoft/TypeScript#18588 and #31148 for progress on this.
   */
  let timeout: any;
  let resolves: ((result: any) => void)[] = [];

  return function (...args: any) {
    clearTimeout(timeout);

    timeout = setTimeout(() => {
      const result = fn(...args);

      resolves.forEach((resolve) => resolve(result));
      resolves = [];
    }, ms);


    return new Promise((resolve) => {
      resolves.push(resolve);
    })
  } as ((...args: Parameters<F>) => Promise<ReturnType<F>>);
}

export function mDebounce (ms: number) {
  return function (
    target: Object,
    propertyKey: string | symbol,
    descriptor: PropertyDescriptor
  ) {
    const map = new WeakMap;
    const originalMethod = descriptor.value;

    descriptor.value = function (...args: any) {
      let debounced = map.get(this);

      if (!debounced) {
        debounced = debounce(originalMethod.bind(this), ms);
        map.set(this, debounced);
      }

      return debounced(...args);
    }

    return descriptor;
  }
}