Once listeners in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a listener that runs only once.

Node.js

emitter.[1]('start', () => { console.log('Started'); });

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

AaddListener

Bon

Conce

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'once' causes the listener to run multiple times.

Using 'emit' instead of a listener method.

The 'once' method adds a listener that is called only the first time the event is emitted.

2fill in blank

medium

Complete the code to emit the 'ready' event once.

Node.js

emitter.[1]('ready');

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Aemit

BaddListener

Conce

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'once' to emit events instead of listen.

Using 'on' which only adds listeners.

The 'emit' method triggers the event and calls listeners.

3fill in blank

hard

Fix the error in adding a one-time listener for 'data' event.

Node.js

emitter.[1]('data', () => { console.log('Data received'); });

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Aon

BremoveListener

Cemit

Donce

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' causes the listener to run multiple times.

Using 'emit' instead of adding a listener.

Use 'once' to add a listener that runs only once for the 'data' event.

4fill in blank

hard

Fill both blanks to add a one-time listener and then emit the event.

Node.js

emitter.[1]('finish', () => { console.log('Finished'); });
emitter.[2]('finish');

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Aonce

Bemit

Con

DremoveListener

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'once' for the listener.

Using 'on' instead of 'emit' to trigger the event.

Use 'once' to add a one-time listener and 'emit' to trigger the event.

5fill in blank

hard

Fill all three blanks to add a one-time listener, emit the event, and verify it runs only once.

Node.js

let count = 0;
emitter.[1]('ping', () => { count++; });
emitter.[2]('ping');
emitter.[3]('ping');
console.log(count);

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

Aonce

Bemit

Con

DremoveListener

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'once' causes count to increase twice.

Using 'once' but not emitting the event.

Use 'once' to add a one-time listener, then 'emit' twice to show the listener runs only once, so count is 1.