response.js

const fetchResponse = (responseId, projectId) => (
  callBizApi(getEndpoints(responseId))
    .then(initialData => {
      const response = initialData.response;
      const taskId = response.taskId;
      const participantId = response.participant.id;

      return callBizApi(getRelationEndpoints(projectId, taskId, participantId))
        .then(relationData => (
          mapResponse({
            response,
            questions: relationData.questions,
            assets: relationData.assets,
            participant: relationData.participant
          })
        ))
        .catch(error => Promise.reject(error));
    })
);

routes.js

router.route('/projects/:projectId/responses/:responseId')
  .get((req, res) => {
    fetchResponse(...R.props(['responseId', 'projectId'], req.params))
      .then(response => res.json(response))
      .catch(sendError(res));
  });