javascript – Why does this angular-node front-end app hang-up when connected to this mongodb-express back-end api?

I have recently discovered RealWorld , which provides front-end and back-end apps to help begin development of a web-app.

I am trying to run a development for a MEAN stack application.
My Development

I have:

  1. logged into MongoDB,
  2. npm run dev on the backend (which correctly returns a route),
  3. ng serve on the frontend (changed api_url in environment.ts to localhost:3000/api).

The issue is that the REST-api is hanging up when trying to load articles or create a user; this is seen in Firefox at the port for the front-end.
Could anyone please give me some guidance?