Issues with multiple async requests

[amaschas]

I am using xhr-promise in a library that requests data via a two-step process that can occur multiple times asynchronously. Each data request involves a query to an API that responds with a data URL. The library then makes a second request to fetch the data from the URL in the first response.

getQueryData(queryID) {
  let xhrPromise = new XMLHttpRequestPromise();
  return xhrPromise.send({
    method: 'GET',
    url: 'http://localhost:3002/v1/query-jobs/' + queryID
  }).then(response => {
    if (response.responseText.done) {
      return this.xhrPromise.send({
        method: 'GET',
        url: response.responseText.document_url
      });
    } else {
      return Promise.resolve(false);
    }
  });
  }

This process works fine if I execute getQueryData once. However, if I execute it twice (which means it's executing asynchronously, in parallel), the second stage of the first request returns with no data. The problem appears to occur in the call to _this._getResponseUrl() in xhr-promise. The response data is present before the call to _getResponseUrl, but once inside the function code block, the referenced xhr is empty.

It's also worth noting that while responseText is empty in object that gets returned by xhr-promise, the reponseText field in the xhr object that gets returned is populated, and JSON therein is valid. I'm currently just using the values in the xhr object in my implementation.