locker.js

export default (concurrency = 1) => {
  let activeConsumerCount = 0;
  const queue = [];

  const consume = async () => {
    if (activeConsumerCount >= concurrency) {
      return;
    }

    activeConsumerCount += 1;

    while (queue.length > 0) {
      const task = queue.shift();

      try {
        task.resolve(await task.run());
      } catch (err) {
        task.reject(err);
      }
    }

    activeConsumerCount -= 1;
  };

  return async (run) => {
    return await new Promise((resolve, reject) => {
      queue.push({ run, resolve, reject });
      consume();
    });
  };
};