Removing listeners in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the listener from the event emitter.

Node.js

emitter.removeListener('data', [1]);

Drag options to blanks, or click blank then click option'

Aonce

BonData

Cemit

DaddListener

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the event name instead of the listener function.

Using addListener instead of the listener function.

Trying to remove a listener that was never added.

The removeListener method requires the exact listener function to remove it. Here, onData is the listener function.

2fill in blank

medium

Complete the code to remove all listeners for the 'end' event.

Node.js

emitter.[1]('end');

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AremoveListener

Boff

Conce

DremoveAllListeners

Attempts:

3 left

💡 Hint

Common Mistakes

Using removeListener which removes only one listener.

Using once which adds a one-time listener.

Using off which is an alias but not always available.

The removeAllListeners method removes all listeners for a specific event.

3fill in blank

hard

Fix the error in removing a listener by completing the code.

Node.js

emitter.off('message', [1]);

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AhandleMessage

BhandleMessage()

C'handleMessage'

DmessageHandler

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function with parentheses which executes it immediately.

Passing the function name as a string instead of a function reference.

Passing a different function name than the one added.

The listener function must be passed as a reference without parentheses or quotes. Using handleMessage passes the function correctly.

4fill in blank

hard

Fill both blanks to remove a listener added with once.

Node.js

const listener = () => console.log('done');
emitter.[1]('finish', listener);
emitter.[2]('finish', listener);

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Aonce

BremoveListener

CremoveAllListeners

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using on instead of once to add the listener.

Using removeAllListeners which removes all listeners, not just one.

Not passing the same listener function to remove it.

The listener is added with once and removed with removeListener by passing the same function reference.

5fill in blank

hard

Fill all three blanks to remove a named listener after adding it.

Node.js

function logData(data) {
  console.log(data);
}
emitter.[1]('data', logData);
emitter.[2]('data', logData);
const count = emitter.listenerCount([3]);

Drag options to blanks, or click blank then click option'

Aon

BremoveListener

C'data'

Donce

Attempts:

3 left

💡 Hint

Common Mistakes

Using once instead of on to add the listener.

Passing the function name as a string instead of the function reference when removing.

Not passing the event name string to listenerCount.

The listener is added with on, removed with removeListener, and the event name 'data' is passed to listenerCount to check remaining listeners.