EventEmitter class in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the <code>EventEmitter</code> class in Node.js?

The <code>EventEmitter</code> class allows objects to emit named events and register functions (listeners) to respond when those events occur. It helps manage asynchronous events easily.

beginner

How do you add a listener function to an event using EventEmitter?

Use the on(eventName, listener) method to register a listener function that runs whenever the specified event is emitted.

beginner

What method do you use to trigger or emit an event in EventEmitter?

Use the emit(eventName, ...args) method to trigger an event and optionally pass arguments to the listener functions.

intermediate

What happens if you emit an event with no listeners attached in EventEmitter?

Nothing happens; the event is emitted but no functions run because no listeners are registered for that event.

intermediate

How can you remove a listener from an event in EventEmitter?

Use the removeListener(eventName, listener) or off(eventName, listener) method to remove a specific listener function from an event.

Which method adds a listener to an event in EventEmitter?

A removeListener()

B emit()

C trigger()

D on()

The on() method registers a listener function for an event.

What does the emit() method do?

A Triggers an event

B Removes a listener

C Creates a new EventEmitter

D Lists all events

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

If no listeners are registered for an event, what happens when you emit it?

A A default listener runs

B An error is thrown

C Nothing happens

D The program crashes

Emitting an event with no listeners does nothing; no functions run.

Which method removes a listener from an event?

A emit()

B off()

C addListener()

D listen()

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

What kind of programming does EventEmitter help manage?

A Asynchronous event-driven programming

B Functional programming

C Procedural programming

D Synchronous programming

EventEmitter helps manage asynchronous event-driven programming by handling events and listeners.

Explain how you would use the EventEmitter class to respond to a custom event in Node.js.

Think about how events and listeners work together.

Describe the difference between the on() and emit() methods in the EventEmitter class.

One sets up a reaction, the other starts the event.