Example use of EventEmitter in Node.js

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Here is an example of how to use the EventEmitter object in node.js …

var EventEmitter = require('events').EventEmitter;
var ee = new EventEmitter;
ee.on('someevent', function() {
	console.log('The someevent happened');
});

// emit the event
ee.emit('someevent');

// emit the event again
ee.emit('someevent');

The output will be …

The someevent happened
The someevent happened

But if you use the “once” instead of “on” as in …

var EventEmitter = require('events').EventEmitter;
var ee = new EventEmitter;
ee.once('someevent', function() {
	console.log('The someevent happened');
});

// emit the event
ee.emit('someevent');

// emit the event again
ee.emit('someevent');

The output will just be …

The someevent happened

because the event handler is invoked only once.

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