Exercise tracker

I created this app as a requirement for my freeCodeCamp APIs and Microservices Certification, using Node.js, Express, Mongoose, shortId, and a free MongoDB Atlas database. The front end API on the home page also uses Bootstrap, jQuery, jQuery UI, and highlight.js. The API fulfills the following user stories:

1. I can create a user by posting form data username to /api/exercise/new-user and returned will be an object with username and _id.
2. I can get an array of all users by getting api/exercise/users with the same info as when creating a user.
3. I can add an exercise to any user by posting form data userId (_id), description, duration, and optionally date to /api/exercise/add. If no date supplied it will use current date. Returned will the the user object with also with the exercise fields added.
4. I can retrieve a full exercise log of any user by getting /api/exercise/log with a parameter of userId (_id). Return will be the user object with added array log and count (total exercise count).
5. I can retrieve part of the log of any user by also passing along optional parameters of from & to or limit. (Date format yyyy-mm-dd, limit = int)