Events

• The events module supports events. Use require('events') to access this module.

Class: EventEmitter

An instance of EventEmitter class will emits events. If you need to define a class emitting events, you can defined a class by extending from EventEmitter.

const { EventEmitter } = require('events');

class MyEmitter extends EventEmitter {}

var myEmitter = new MyEmitter();

myEmitter.on('event', () => {
  console.log('event occurred!');
});

myEmitter.emit('event');

emitter.addListener(eventName, listener)

• eventName {string} The name of event
• listener {function} The callback function

Add the listener function to the end of the listener array for the event named eventName.

server.addListener('connect', function () {
  // equivalent to server.on
  console.log('server connected');
});

emitter.emit(eventName[, ...args])

• eventName {string} The name of event
• ...args {any} Arguments to be passed to the listener functions.

Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

server.on('data', function (data) {
  console.log(data); // "data received"
});

var data = 'data recived';
server.emit('data', data);

emitter.on(eventName, listener)

• eventName {string} The name of event.
• listener {function} The callback function.

Alias for emitter.addListener(eventName, listener).

server.on('connect', function () {
  console.log('server connected');
});

emitter.once(eventName, listener)

• eventName {string} The name of event.
• listener {function} The callback function.

Add one-time listener for the event named eventName. When the event is triggered, the listener function is called and then removed from the listener array of the event.

server.once('connect', function () {
  console.log('connected');
});

server.emit('connect'); // 'connected' printed
server.emit('connect'); // nothing printed

emitter.removeListener(eventName, listener)

• eventName {string} The name of event.
• listener {function} The callback function.

Remove the listener function from the listener array of the event name eventName.

function connectListener () {
  console.log('connected');
}

server.addListener('connect', connectListener); // eq to server.on
server.emit('connect'); // 'connected' printed

server.removeListener('connect' connectListener); // eq to server.off
server.emit('connect'); // nothing printed

emitter.removeAllListeners([eventName])

• eventName {string}

Remove all listeners of the event named eventName.

emitter.off(eventName, listener)

• eventName {string} The name of event.
• listener {function} The callback function

Alias for emitter.removeListener(eventName, listener).

emitter.listeners(eventName)

• eventName {string} The name of event.
• Returns: {Array<Function>}

Return all listeners of the given event.

emitter.listenerCount(eventName)

• eventName {string} The name of event.
• Returns: {number}

Return the number of listeners of the given event.