An Oak application is most often used as a backend application in a client-server architecture whereas the client could be written in React.js or another popular frontend solution and the server could be written in Oak. Both entities result in a client-server architecture (frontend and backend relationship) whereas the backend would be needed for (A) business logic that shouldn’t be exposed as source code to the frontend application – otherwise it would be accessible in the browser – or for (B) establishing connections to third-party data sources (e.g. database(s)).

However, don’t mistake client application always for frontend and server application always for backend here. These terms cannot be exchanged that easily. Whereas a frontend application is usually something seen in the browser, a backend usually performs business logic that shouldn’t be exposed in a browser and often connects to a database as well.

Frontend -> Backend -> Database

But, in contrast, the terms client and server are a matter of perspective. A backend application (Backend 1) which consumes another backend application (Backend 2) becomes a client application (Backend 1) for the server application (Backend 2). However, the same backend application (Backend 1) is still the server for another client application which is the frontend application (Frontend).

Frontend -> Backend 1 -> Backend 2 -> Database

// Frontend: Client of Backend 1
// Backend 1: Server for Frontend, also Client of Backend 2
// Backend 2: Server for Backend 1

If you want to answer the client-server question if someone asks you what role an entity plays in a client-server architecture, always ask yourself who (server) is serving whom (client) and who (client) consumes whom’s (backend) functionalities?

That’s the theory behind client-server architectures and how to relate to them. Let’s get more practical again. How do client and server applications communicate with each other? Over the years, there existed a few popular communication interfaces (APIs) between both entities. However, the most popular one is called REST defined in 2000 by Roy Fielding. It’s an architecture that leverages the HTTP protocol to enable communication between a client and a server application. A server application that offers a REST API is also called a RESTful server. Servers that don’t follow the REST architecture a 100% are rather called RESTish than RESTful. In the following, we are going to implement such REST API for our Oak server application, but first let’s get to know the tooling that enables us to interact with a REST API.

#deno #oak #rest #api #web-development