In this recipe, you will build a RESTful API that will allow the creation of new users, log in, display user information, and delete a user's profile. Furthermore, you will learn how to build a NodeJS REPL with a client API that you can use to interact with your server's RESTful API.

A REPL (Read-Eval-Print Loop) is like an interactive shell where you can execute commands one after another. For instance, the Node.js REPL can be opened by running this command in your terminal:

node -i 

Here, the -i flag stands for interactive. Now, you can execute the JavaScript code that gets evaluated piece by piece in a new context.