Debounce promise-returning & async functions

debounceAsync.ts

/**
 * A function that emits a side effect and returns a promise.
 */
type Procedure = (...args: any[]) => Promise<void>;

/**
 * `debounceAsync` debounces promise-returning & async functions.
 * Adapted from Sindre's p-debounce.
 * Ref: https://github.com/sindresorhus/p-debounce
 *
 * @param functionToDebounce - Promise-returning/async function.
 * @param wait - Milliseconds to wait before calling `functionToDebounce` again.
 * @returns A function that delays calling `functionToDebounce` until after
 * `wait` milliseconds have elapsed since the last time it was called.
 */
function debounceAsync(
  functionToDebounce: Procedure,
  wait: number = 250
): Procedure {
  let timer: NodeJS.Timer | null;
  let resolveList: any[] = [];

  return (...args) => {
    const context = this;

    return new Promise(resolve => {
      clearTimeout(timer);

      timer = setTimeout(() => {
        timer = null;

        const result = functionToDebounce.apply(context, args);

        for (resolve of resolveList) {
          resolve(result);
        }

        resolveList = [];
      }, wait);

      !timer
        ? resolve(functionToDebounce.apply(context, args))
        : resolveList.push(resolve);
    });
  };
}