50-Nodejs Course 2023: Events Driven Architecture: Introduction

Introduction

Event Driven Architecture is a software architecture pattern that uses events to trigger actions. It is a very popular pattern in the industry and it is used in many applications. In this course, we will learn how to use it in Nodejs.

To Read more about it, see my Event Driven Architecture: A Practical Guide in Javascript Article.

Usage in our Application

Now let's move to the practical part. We will use it in our application to handle the following use cases:

But first we need an event emitter. We will use the Mongez Events class from Nodejs.

Why? Is it a narcissism? Actually no, but i can assure you that this is the easiest event emitter that you will ever use. It is very simple and straight.

Let's see a simple example:

import events from '@mongez/events';

events.subscribe('delivered', (food) => {
  // this will be called when the event is fired
  console.log('Delivered', food); // Delivered Pizza
});

events.trigger('delivered', 'Pizza');

So we basically subscribe to the event (before the trigger) to listen to it, and then we trigger it (after the subscription) to fire the event.

Event Unsubscription

We can unsubscribe from an event by using the unsubscribe method:

import events from '@mongez/events';

const eventSubscription = events.subscribe('delivered', (food) => {
  // this will be called when the event is fired
  console.log('Delivered', food); // Delivered Pizza
});

events.trigger('delivered', 'Pizza');

eventSubscription.unsubscribe(); // once unsubscribed, the callback will not be called anymore

events.trigger('delivered', 'Pizza'); // this will not be called

So far so good, but what if we want to unsubscribe from all events? We can do that by using the unsubscribe method:

import events from '@mongez/events';

events.subscribe('delivered', (food) => {
  // this will be called when the event is fired
  console.log('Delivered', food); // Delivered Pizza
});

events.trigger('delivered', 'Pizza');

events.unsubscribe('delivered'); // once unsubscribed, the callback will not be called anymore

events.trigger('delivered', 'Pizza'); // this will not be called