Web application programming interfaces (APIs) have become more and more popular, as more people have started to recognize the need to separate their server-side applications from their client-side applications. APIs give developers the opportunity to offer the same web services to multiple clients, while also reducing the coupling between their systems.

In this chapter, we will build a REST API using Koa. We will make use of the different Koa concepts that we covered in the previous chapters in order to build a full-fledged API.

The API that we will build will be for managing contacts. We will be able to perform create, read, update, and delete (CRUD) operations on contacts in our database via the API. We will persist and retrieve data to and from a MongoDB database, using Mongoose. We will also make use of Nodemon to debug our applications, and Postman...