node.js: emitter.on(eventName, listener)

emitter.on(eventName, listener)

It adds a listener to this event.

HelloWorld.js

var util = require('util');

var EventEmitter = require('events').EventEmitter;

var emitter = new EventEmitter();

emitter.on('sayHello', () => {
 console.log("Hello World");
});

emitter.emit('sayHello');

Output

Hello World

You can add more than one listener to the event. ‘on’ method adds the listener function to the end of the listeners array for the event named eventName.

HelloWorld.js

var util = require('util');

var EventEmitter = require('events').EventEmitter;

var emitter = new EventEmitter();

emitter.on('sayHello', () => {
 console.log("Hello World");
});

emitter.on('sayHello', (name) => {
 console.log("Hello mr.%s, How are you?", name);
});

emitter.emit('sayHello', "Krishna");

Output

Hello World

Hello mr.Krishna, How are you?

Note

a.   ‘on’ method returns a reference to the EventEmitter, so that calls can be chained.

b.   Event listeners are invoked in the order they called.

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