Custom event emitter classes in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom event emitter class in Node.js?

A custom event emitter class is a user-defined class that extends Node.js's built-in EventEmitter to create and manage custom events, allowing different parts of an app to communicate by emitting and listening to events.

beginner

How do you create a custom event emitter class in Node.js?

You create a custom event emitter class by importing { EventEmitter } from the 'events' module and extending it with your class. Then you can add methods that emit events using this.emit('eventName').

intermediate

Why use custom event emitter classes instead of plain callbacks?

Custom event emitters allow multiple listeners for the same event, better organization of event logic, and decoupling of code parts. Callbacks are limited to single responses and can get messy with many events.

beginner

What method do you use to listen for an event in a custom event emitter class?

You use the .on('eventName', callback) method to listen for an event. The callback runs whenever the event is emitted.

intermediate

How can you remove an event listener from a custom event emitter?

You can remove a listener using the .off('eventName', callback) method or .removeListener('eventName', callback). This stops the callback from running when the event fires.

Which Node.js module do you extend to create a custom event emitter class?

A http

B events

C fs

D stream

The 'events' module provides the EventEmitter class, which you extend to create custom event emitters.

What method do you call to emit an event in a custom event emitter?

A emit()

B on()

C listen()

D trigger()

The emit() method triggers an event and calls all listeners attached to that event.

How do you add a listener for an event named 'data'?

A on('data', callback)

B emit('data', callback)

C listen('data', callback)

D addListener('callback', 'data')

The on() method attaches a callback function to the 'data' event.

What happens if multiple listeners are attached to the same event?

A Only the last listener runs

B Only the first listener runs

C All listeners run in the order they were added

D Listeners run randomly

All listeners for an event run in the order they were added when the event is emitted.

Which method removes a specific listener from an event?

A addListener()

B emit()

C on()

D off()

The off() method removes a specific listener callback from an event.

Explain how to create and use a custom event emitter class in Node.js.

Think about how classes and events work together.

Describe the benefits of using custom event emitter classes over simple callbacks.

Consider how events help different parts of an app talk to each other.