AbortController for cancellation in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new AbortController instance.

Node.js

const controller = new [1]();

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

APromise

BAbortSignal

CEventEmitter

DAbortController

Attempts:

3 left

💡 Hint

Common Mistakes

Using AbortSignal instead of AbortController.

Using Promise which is unrelated here.

The AbortController is used to create a controller that can abort asynchronous tasks.

2fill in blank

medium

Complete the code to get the signal from the AbortController.

Node.js

const signal = controller.[1];

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

Aabort

Bcancel

Csignal

Dcontroller

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'abort' which is a method, not a property.

Using 'cancel' which does not exist.

The signal property of the controller provides the signal to pass to async tasks for cancellation.

3fill in blank

hard

Fix the error in the code to abort the controller.

Node.js

controller.[1]();

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

Aabort

Bcancel

Cstop

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cancel' which is not a method of AbortController.

Using 'stop' or 'end' which do not exist.

The abort() method triggers the cancellation signal.

4fill in blank

hard

Fill both blanks to create a fetch request that can be aborted.

Node.js

fetch(url, { signal: [1] }).then(response => response.[2]());

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

Asignal

Bjson

Ctext

Dcontroller

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the controller instead of its signal.

Using 'text' instead of 'json' when expecting JSON data.

The signal property is passed to fetch for cancellation, and json() parses the response body.

5fill in blank

hard

Fill all three blanks to handle abort error in a fetch request.

Node.js

try {
  await fetch(url, { signal: [1] });
} catch (error) {
  if (error.[2] === '[3]') {
    console.log('Fetch aborted');
  }
}

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

Asignal

Bname

CAbortError

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Checking error.message instead of error.name.

Passing controller instead of signal.

The signal is passed to fetch. The error's name property is checked for 'AbortError' to detect cancellation.

Practice

1. What is the main purpose of AbortController in Node.js?

easy

A. To manage file system permissions

B. To create new HTTP servers

C. To cancel ongoing asynchronous operations like fetch requests

D. To handle database connections

Solution

1. Step 1: Understand AbortController's role

   AbortController is designed to stop or cancel asynchronous tasks such as fetch requests.

2. Step 2: Compare with other options

   Creating servers, managing permissions, or handling databases are unrelated to AbortController's purpose.

3. Final Answer:

   To cancel ongoing asynchronous operations like fetch requests -> Option C

4. Quick Check:

   AbortController cancels async tasks = C [OK]

Hint: AbortController is about stopping async tasks quickly [OK]

Common Mistakes:

• Confusing AbortController with server or database management
• Thinking it manages permissions
• Assuming it creates servers

2. Which of the following is the correct way to create an AbortController and get its signal?

easy

A. const signal = new AbortController.signal();

B. const controller = new AbortController; const signal = controller.abort();

C. const controller = AbortController(); const signal = controller.abort;

D. const controller = new AbortController(); const signal = controller.signal;

Solution

1. Step 1: Check correct instantiation syntax

   AbortController must be created with 'new AbortController()' and its signal accessed via 'controller.signal'.

2. Step 2: Identify errors in other options

   const signal = new AbortController.signal(); wrongly calls signal as a constructor. const controller = AbortController(); const signal = controller.abort; misses 'new' and uses 'abort' instead of 'signal'. const controller = new AbortController; const signal = controller.abort(); misses parentheses on 'new AbortController()' and calls 'abort()' instead of accessing 'signal'.

3. Final Answer:

   const controller = new AbortController(); const signal = controller.signal; -> Option D

4. Quick Check:

   Use 'new' and access 'signal' property = B [OK]

Hint: Always use 'new AbortController()' and get 'signal' property [OK]

Common Mistakes:

• Forgetting 'new' keyword
• Calling 'abort' instead of accessing 'signal'
• Treating 'signal' as a constructor

3. What will be the output of this code snippet?

const controller = new AbortController();
const signal = controller.signal;

setTimeout(() => controller.abort(), 100);

signal.addEventListener('abort', () => console.log('Aborted!'));

medium

A. Logs 'Aborted!' after 100 milliseconds

B. Logs 'Aborted!' immediately

C. Throws an error immediately

D. No output, because abort is never called

Solution

1. Step 1: Understand the abort timing

   The controller.abort() is called after 100 milliseconds using setTimeout.

2. Step 2: Check event listener behavior

   The signal listens for 'abort' event and logs 'Aborted!' when triggered.

3. Final Answer:

   Logs 'Aborted!' after 100 milliseconds -> Option A

4. Quick Check:

   Abort triggers event after delay = D [OK]

Hint: Abort triggers event after delay, not immediately [OK]

Common Mistakes:

• Assuming abort happens immediately
• Expecting no output because of async delay
• Thinking it throws error instead of event

4. Identify the error in this code snippet that uses AbortController:

const controller = new AbortController();
const signal = controller.signal;

fetch('https://example.com', { signal });
controller.abort();

signal.addEventListener('abort', () => console.log('Fetch aborted'));

medium

A. Not passing the signal to fetch options

B. Calling abort() before adding the abort event listener

C. Using signal.addEventListener instead of controller.addEventListener

D. Missing async/await for fetch

Solution

1. Step 1: Check event listener timing

   The abort event listener is added after calling controller.abort(), so it misses the event.

2. Step 2: Verify other parts

   The signal is correctly passed to fetch, and signal is the right object to listen on. Async/await is optional here.

3. Final Answer:

   Calling abort() before adding the abort event listener -> Option B

4. Quick Check:

   Add event listener before abort() call = A [OK]

Hint: Add abort listener before calling abort() [OK]

Common Mistakes:

• Adding listener after abort() call
• Listening on controller instead of signal
• Forgetting to pass signal to fetch

5. You want to cancel a fetch request if it takes longer than 200ms. Which code correctly implements this using AbortController?

hard

A. const controller = new AbortController();
setTimeout(() => controller.abort(), 200);
fetch('https://api.com/data', { signal: controller.signal })
.catch(err => { if (err.name === 'AbortError') console.log('Request timed out'); });

B. const controller = new AbortController();
fetch('https://api.com/data', { signal: controller.signal });
setTimeout(() => controller.abort(), 200);
console.log('Request timed out');

C. const controller = new AbortController();
fetch('https://api.com/data');
setTimeout(() => controller.abort(), 200);
.catch(err => console.log('Request timed out'));

D. const controller = new AbortController();
setTimeout(() => controller.abort(), 200);
fetch('https://api.com/data', { signal: controller.abort() })
.catch(err => console.log('Request timed out'));

Solution

1. Step 1: Setup AbortController and timeout

   Create controller, set timeout to call abort after 200ms.

2. Step 2: Pass signal to fetch and handle abort error

   Pass controller.signal to fetch options and catch AbortError to log timeout message.

3. Step 3: Identify errors in other options

   const controller = new AbortController(); fetch('https://api.com/data', { signal: controller.signal }); setTimeout(() => controller.abort(), 200); console.log('Request timed out'); logs timeout immediately, not on abort. const controller = new AbortController(); fetch('https://api.com/data'); setTimeout(() => controller.abort(), 200); .catch(err => console.log('Request timed out')); misses passing signal. const controller = new AbortController(); setTimeout(() => controller.abort(), 200); fetch('https://api.com/data', { signal: controller.abort() }) .catch(err => console.log('Request timed out')); incorrectly calls abort() instead of passing signal.

4. Final Answer:

   const controller = new AbortController(); setTimeout(() => controller.abort(), 200); fetch('https://api.com/data', { signal: controller.signal }) .catch(err => { if (err.name === 'AbortError') console.log('Request timed out'); }); -> Option A

5. Quick Check:

   Pass signal, abort after delay, catch AbortError = A [OK]

Hint: Pass controller.signal to fetch and abort after timeout [OK]

Common Mistakes:

• Calling abort() instead of passing signal
• Logging timeout before abort happens
• Not passing signal to fetch