How to properly queue requests in javascript with a delay?

Question

JavaScript

There is a set of http requests, how to execute them in order, with a delay?
UPD1 : At the moment such a solution is written, but there is a fear that there will be memory leaks
UPD2 : There are no memory leaks.

class Balancer {
  constructor(kwArr, timeout) {
    this._i = 0;

    this._kwArr = kwArr;
    this._tikTimeout = timeout;

    this.start();
  }

  start() {
    this._instance = setInterval( () => { this._tik(); }, this._tikTimeout );
  }

  stop() {
     clearInterval(this._instance);
  }

  _tik() {
    if(this._i < this._kwArr.length) {
      var kw = this._kwArr[this._i++];
      requestFunc(kwArr.url);
    } else {
      this.stop();
    }
  }
}

Answer 1

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

function doRequest(urls){
  var url = urls.shift();

  if( ! url){
    return Promise.resolve();
  }

  return request(url)
    .then(() => {
      return sleep(5000);
    })
    .then(() => {
      return doRequest(urls);
    });
}

doRequest([
  'http://google.com',
  'http://ya.ru'
])
.then(() => {
  // complete
})
.catch(err => {
  console.error(err);
})