Every action on a computer is an event. The system produces (or "fires") a signal of some kind when an event occurs, and provides a mechanism by which an action can be automatically taken (that is, some code running) when the event occurs. Events are fired inside the browser window and tend to be attached to a specific item that resides in it. This might be a single element, a set of elements, the HTML document loaded in the current tab, or the entire browser window. Many different types of events can occur.
For example:
Objects in Node.js can fire events like the read Stream object fires events when opening and closing a file:
var fs = require('fs');
var rs = fs.createReadStream('./demofile.txt');
rs.on('open', function () {
console.log('The file is open');
});
Events Module
Node.js has a built-in module, called "Events", where you can create-, fire-, and listen for- your own events.
To include the built-in Events module use the require() method. In addition, all event properties and methods are an instance of an EventEmitter object. To be able to access these properties and methods, create an EventEmitter object:
var events = require('events');
var eventEmitter = new events.EventEmitter();
The EventEmitter Object
You can assign event handlers to your own events with the EventEmitter object.
In the example below 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 eventEmitter = new events.EventEmitter();
//Create an event handler:
var myEventHandler = function () {
console.log('I hear a scream!');
}
//Assign the event handler to an event:
eventEmitter.on('scream', myEventHandler);
//Fire the 'scream' event:
eventEmitter.emit('scream');