storyblok-js-client/src/throttlePromise.ts

Universal JavaScript SDK for Storyblok's API

import type { ISbThrottle, Queue } from './interfaces';

class AbortError extends Error {
  constructor(msg: string) {
    super(msg);
    this.name = 'AbortError';
  }
}

function throttledQueue<T extends (...args: Parameters<T>) => ReturnType<T>>(
  fn: T,
  limit: number,
  interval: number,
): ISbThrottle<T> {
  if (!Number.isFinite(limit)) {
    throw new TypeError('Expected `limit` to be a finite number');
  }

  if (!Number.isFinite(interval)) {
    throw new TypeError('Expected `interval` to be a finite number');
  }

  const queue: Queue<Parameters<T>>[] = [];
  let timeouts: ReturnType<typeof setTimeout>[] = [];
  let activeCount = 0;
  let isAborted = false;

  const next = async () => {
    activeCount++;

    const x = queue.shift();
    if (x) {
      try {
        const res = await fn(...x.args);
        x.resolve(res);
      }
      catch (error) {
        x.reject(error);
      }
    }

    const id = setTimeout(() => {
      activeCount--;

      if (queue.length > 0) {
        next();
      }

      timeouts = timeouts.filter(currentId => currentId !== id);
    }, interval);

    if (!timeouts.includes(id)) {
      timeouts.push(id);
    }
  };

  const throttled: ISbThrottle<T> = (...args) => {
    if (isAborted) {
      return Promise.reject(
        new Error(
          'Throttled function is already aborted and not accepting new promises',
        ),
      );
    }

    return new Promise((resolve, reject) => {
      queue.push({
        resolve,
        reject,
        args,
      });

      if (activeCount < limit) {
        next();
      }
    });
  };

  throttled.abort = () => {
    isAborted = true;
    timeouts.forEach(clearTimeout);
    timeouts = [];

    queue.forEach(x =>
      x.reject(() => new AbortError('Throttle function aborted')),
    );
    queue.length = 0;
  };

  return throttled;
}

export default throttledQueue;