DispatchQueue for managing request rate against an API call

DispatchQueue.js

import sleep from 'sleep-promise';

class DispatchQueue {
  constructor(rateLimitInSeconds) {
    this.rateLimit = rateLimitInSeconds * 1000;
    this.queueSize = 0;
  }

  async dispatch(call) {
    this.queueSize++;
    const dispatcher = this;
    return new Promise(
      async function (resolve, reject) {
        await sleep(dispatcher.queueSize * dispatcher.rateLimit);
        const result = await call();
        dispatcher.queueSize--;
        resolve(result);
      }
    )
  }
}

async function apiCall() {
  await sleep(100);
  return 'response';
}

(async function main() {
  var d = new DispatchQueue(1);
  for (var i = 0; i < 5; i++) {
    // should observe these resolvers will not all be called at once.
    d.dispatch(apiCall).then(
      function(val) {
        console.log(val);
      }
    );
  }
})();