lib/classes/PromiseTracker.js/PromiseTracker/add
class PromiseTracker:  add(variable, prms, specifier) {
    const promise = prms;
    promise.waitList = `${variable} waited on by: ${specifier}`;
    promise.state = 'pending';
    promise.then(
      // creates a promise with the following effects but that we otherwise ignore
      () => {
        promise.state = 'resolved';
      },
      () => {
        promise.state = 'rejected';
      }
    );
    this.promiseList.push(promise);
    this.promiseMap[variable] = promise;
    return promise;
  }