var Observable = Rx.Observable;

​

function mockHTTPRequest(url) {

    return Observable.of(`Response from ${url}`)

      .delay(1000);

}

​

function timestamp() {

  return (new Date()).getTime() - start;

}

​

var start = (new Date()).getTime();

​

Observable.of('url-1') 

  .concatMap(url => {

    console.log(timestamp() + ': Sending request to ' + url);

    return mockHTTPRequest(url);

  })

  .do(response => console.log(timestamp() + ': ' + response))

​

  .concatMap(response => {

    console.log(timestamp() + ': Sending request to ' + response);

    let newUrl = 'url-' + response.length; // create new requests url

    return mockHTTPRequest(newUrl);

  })

  .do(response => console.log(timestamp() + ': ' + response))

​

  .concatMap(response => {

    console.log(timestamp() + ': Sending request to ' + response);

    let newUrl = 'url-' + response.length; // create another requests url

    return mockHTTPRequest(newUrl);

  })

  .subscribe(response => console.log(timestamp() + ': ' + response));

​

​