Achieving separation of concerns using Events in Node.js

Separation of Concerns (SoC) one of the important concepts in software design and architecture, it's about decomposing the system into parts that highly independent and slightly overlapping in functionality.

*Separation of Concerns (SoC) *one of the important concepts in software design and architecture, it's about decomposing the system into parts that highly independent and slightly overlapping in functionality.

In the case of OOP languages, *encapsulation *and *inheritance *are one of the main ways to achieve SoC. *Event-Driven Programming (EDP) *can be also a major concept in SoC too, ideally, the modules that are throwing the events should not be aware of the modules that will handle them. In this article, I will take you through implementing EDP in *NodeJS *with a real-life example.

Basic concepts with example

I will talk about an AI system that processes inputs, move across a couple of states, and do actions accordingly. I can give an example of that in reinforcement learning through the Q-learning algorithm.

While the core idea about the Q-learning algorithm is using rewards to optimize the knowledge base of the agent, then action execution would be another topic that can be separated apart from the learning procedure.

And an example of that is the Pacman game where the actions will be confined in the following list (Move up- Move down — Move left — Move right) and the SoC will be achieved by separating the Q-Learning algorithm implementation and applying actions to the screen to move the Pacman to one of the directions.

In my example, I will use a very interesting library to implement the event-driven system:

EventEmitter component inside that library supports the ability to dispatch events through “emit” function and to attach handlers to the events using “on” function, and we will talk next more about these concepts next.

An Events-driven system composed usually from the following parts:

• Event: The type of event that can occur inside the system, in our case (Top, bottom, Left, Right) and that can be implemented using an enum, I implemented that inside events.js file that exports the following object which composed of only key-value pairs, a good practice would be to use Object.freeze() on that object if you don’t want anyone by mistake to modify on it:

software-engineering software-development programming javascript nodejs

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