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NODEJS EVENTEMITTER HOW TO

The output in the console will be as follows: an event occurred! When the event ‘eventOne’ is emitted, both the above callbacks should be invoked. MyEmitter.on('eventOne', c2) // Register for eventOne

MyEmitter.on('eventOne', c1) // Register for eventOne Example 1 - Create an event emitter instance and register a couple of callbacks const myEmitter = new EventEmitter() Ĭonsole.log('yet another event occurred!') In fact, if you replace our EventEmitter with Node.js’s built-in ‘events’ module you will get the same result. Please note that our code will mimic the exact API of the Node.js ‘events’ module. The above basic features are sufficient to implement a full system using the eventing model.īefore we get into the coding, let’s take a look at how we will be using the EventEmitter class. What we will be building in this tutorial It’s kind of like a pub/sub or observer design pattern (though not exactly).

Registering and unregistering listener functions.

So, an emitter object basically has two main features: The concept is quite simple: emitter objects emit named events that cause previously registered listeners to be called. Many of Node’s built-in modules inherit from EventEmitter including prominent frameworks like Express.js. EventEmitter is at the core of Node asynchronous event-driven architecture. The EventEmitter is a module that facilitates communication/interaction between objects in Node.

Event Emitters play a very important role in the Node.js ecosystem. You can check out my article All About Core Node.JS, for example.īut without further ado, let's get to the topic under discussion: “Event Emitters”. If you are new to Node.js there are many tutorials here on Medium and elsewhere.

NODEJS EVENTEMITTER HOW TO

By Rajesh Pillai How to code your own event emitter in Node.js: a step-by-step guide Understand Node internals by coding small packages/modules Mastering the Node.JS Internals