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Node.js Tutorial » Node.js Event emitter

What is NodeJS Event emitter?

First: Every action on a computer is an event as: when a connection is made or a file is opened

EventEmitter is a module that facilitates communication / interaction between objects in Nodejs.
EventEmitter is at the heart of Node js event-based asynchronous architecture.
Many of Node js' built-in modules inherit from EventEmitter, including prominent frameworks such as Express.js.

The concept is simple: the emitter objects emit named events that cause listeners of previously recorded listeners to call. So an emitting object has practically two main characteristics:

Syntax

const EventEmitter = require('events');

 

Create an event emitter

Create an event emitter instance and register a couple of callbacks

const my_Emitter = new EventEmitter();

function a1() {
console.log('an event occurred now!');
}

function a2() {
console.log('yet another event occurred now!');
}

my_Emitter.on('eventDue', a1); // Register for eventOne
my_Emitter.on('eventDue', a2); // Register for eventOne

When the event ‘eventDue’ is emitted, both the above callbacks should be invoked.

my_Emitter.emit('eventDue');

Output: in the console will be as:

an event occurred now!
yet another event occurred now!

Related subjects:
node.js http module node.js modules global objects nodejs

 

Tags: Node.js Event emitter, event emitter on, once, async, use cases, between modules, singleton, eventemitter off, source code, eventemitter memory leak
What is NodeJS event emitter?
What is event and event emitter?
How do I use EventEmitter in node JS?
What is the use of event emitter?

 

Event with callback parameters

Registering for the event with callback parameters

my_Emitter.on('status', (code, msg)=> console.log(`Got ${code} and ${msg}`));

Emitting the event with parameters:

my_Emitter.emit('status', 400, 'ok');

Output:
in the console will have as below:

Got 400 and ok

Unregistering events

my_Emitter.off('eventDue', a1);

Now if you emit the event as follows, nothing will happen and it will be a noop:

my_Emitter.emit('eventDue); // noop

 

The EventEmitter Object

You can assign event handlers to your own events with the EventEmitter object.

we have created a function that will be executed when a "scream" event is fired.
To fire an event, use the emit() method.

Example:
var events = require('events');
var event_Emitter = new events.Event_Emitter();

//Create an event handler:
var my_Event_Handler = function () {
console.log('Hi, this is my sacript');
}

//Assign the event handler to an event:
event_Emitter.on('script', my_Event_Handler);

//Fire the 'script' event:
event_Emitter.emit('script');

Output:

E:\Users\My_Name>node demo_text_eventemitter.js
Hi, this is my sacript

 



Node.js Event emitter, event emitter on, once, async, use cases, between modules, singleton, eventemitter off, source code, eventemitter memory leak
What is NodeJS event emitter?
What is event and event emitter?
How do I use EventEmitter in node JS?
What is the use of event emitter?

Node.js Event emitter - nodejs

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