Throttles the number of concurrent calls to a promise function

throttlePromiseFn.js

const throttlePromiseFn = module.exports = (fn, { max = 8, PromiseConstructor = Promise } = {}) => {
  const queue = [];
  let count = 0;
  const call = (params, resolve, reject) => {
    const promise = fn(...params);
    promise.then((value)=>{
      checkQueue();
      typeof resolve === 'function' && resolve(value);
    }).catch((reason)=>{
      checkQueue();
      typeof reject === 'function' && reject(reason);
    });
    return promise;
  }
  const checkQueue = () => {
    count--;
    const next = queue.pop();
    if(next){
      count++;
      call(next.params, next.resolve, next.reject);
    }
  }
  const wrapper = (...params) => {
    if(count < max){
      count++;
      return call(params);
    }else{
      return new PromiseConstructor((resolve, reject)=>{
        queue.unshift({ params, resolve, reject });
      });
    }
  }
  return wrapper;
}