AbortController for cancellation in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new AbortController instance.

React Native

const controller = new [1]();

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

AEventController

BAbortSignal

CAbortController

DCancelController

Attempts:

3 left

💡 Hint

Common Mistakes

Using AbortSignal instead of AbortController

Using a non-existent controller name

The AbortController is used to create a controller that can abort fetch requests.

2fill in blank

medium

Complete the code to pass the abort signal to the fetch request.

React Native

fetch(url, { signal: [1].signal })

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

Acontroller

Babort

Csignal

Dcancel

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'signal' directly without the controller

Passing 'abort' or 'cancel' which are not valid

The signal property of the AbortController instance is passed to fetch to enable cancellation.

3fill in blank

hard

Fix the error in the code to abort the fetch request correctly.

React Native

controller.[1]();

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

Acancel

Bterminate

Cstop

Dabort

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cancel()' instead of 'abort()'

Using 'stop()' or 'terminate()' which do not exist

The correct method to cancel a fetch request is abort() on the controller.

4fill in blank

hard

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

React Native

const controller = new [1]();
fetch(url, { signal: [2].signal });

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

AAbortController

Bcontroller

CAbortSignal

Dsignal

Attempts:

3 left

💡 Hint

Common Mistakes

Using AbortSignal instead of AbortController for creation

Passing 'signal' string instead of the controller variable

First, create an AbortController instance, then pass its signal property to fetch.

5fill in blank

hard

Fill all three blanks to handle fetch cancellation with error catching.

React Native

const controller = new [1]();

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

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

AAbortController

Bcontroller

CAbortError

DCancelError

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'CancelError' instead of 'AbortError'

Not passing the controller.signal to fetch

Not creating an AbortController instance

Create an AbortController, pass its signal to fetch, and catch the error named AbortError when aborted.

Practice

1. What is the main purpose of using AbortController in React Native fetch requests?

easy

A. To cancel an ongoing fetch request before it completes

B. To speed up the fetch request automatically

C. To retry a fetch request multiple times

D. To cache the fetch response for offline use

Solution

1. Step 1: Understand what AbortController does

   AbortController provides a way to stop a fetch request that is still running.

2. Step 2: Compare options with AbortController's purpose

   Only To cancel an ongoing fetch request before it completes describes stopping or canceling a fetch request early.

3. Final Answer:

   To cancel an ongoing fetch request before it completes -> Option A

4. Quick Check:

   AbortController cancels fetch = B [OK]

Hint: AbortController is for stopping fetch early [OK]

Common Mistakes:

• Thinking it speeds up fetch automatically
• Confusing cancellation with retry
• Assuming it caches data

2. Which of the following is the correct way to create an AbortController and pass its signal to a fetch request?

easy

A. const controller = new AbortController(); fetch(url, { cancelToken: controller });

B. const controller = AbortController(); fetch(url, { abort: controller });

C. const controller = new AbortController(); fetch(url, { signal: controller })

D. const controller = new AbortController(); fetch(url, { signal: controller.signal });

Solution

1. Step 1: Check how to instantiate AbortController

   It must be created with the new keyword: new AbortController().

2. Step 2: Verify how to pass the signal to fetch

   The fetch option key is signal and its value is controller.signal.

3. Final Answer:

   const controller = new AbortController(); fetch(url, { signal: controller.signal }); -> Option D

4. Quick Check:

   Use new and pass signal property = C [OK]

Hint: Use new AbortController() and pass signal: controller.signal [OK]

Common Mistakes:

• Omitting the new keyword
• Passing controller instead of controller.signal
• Using wrong option keys like abort or cancelToken

3. Consider this code snippet:

const controller = new AbortController();
fetch('https://example.com/data', { signal: controller.signal })
  .then(response => response.json())
  .then(data => console.log('Data:', data))
  .catch(error => console.log('Error:', error.name));

controller.abort();

What will be logged to the console?

medium

A. Error: AbortError

B. Data: [fetched data]

C. Error: TypeError

D. Nothing is logged

Solution

1. Step 1: Understand what controller.abort() does

   Calling abort() cancels the fetch request, triggering an error with name 'AbortError'.

2. Step 2: Check the catch block behavior

   The catch block logs the error name, so it will log 'AbortError'.

3. Final Answer:

   Error: AbortError -> Option A

4. Quick Check:

   Abort triggers AbortError catch = A [OK]

Hint: Aborting fetch triggers AbortError in catch [OK]

Common Mistakes:

• Expecting data to log after abort
• Confusing AbortError with TypeError
• Thinking nothing logs on abort

4. You wrote this code but the fetch never cancels as expected:

const controller = new AbortController();
fetch('https://api.example.com', { signal: controller.signal });
// Some code
controller.abort();

What is the most likely reason the fetch is not canceled?

medium

A. You did not assign the signal property correctly

B. You called abort() before starting fetch

C. The fetch request already completed before abort() was called

D. You forgot to handle the abort error in catch block

Solution

1. Step 1: Understand timing of abort()

   If abort() is called after fetch completes, it has no effect.

2. Step 2: Check other options

   Signal is assigned correctly, and abort() is called after fetch starts, so those are not issues.

3. Final Answer:

   The fetch request already completed before abort() was called -> Option C

4. Quick Check:

   Abort after fetch finishes does nothing = A [OK]

Hint: Abort only works if fetch is still running [OK]

Common Mistakes:

• Ignoring fetch completion timing
• Assuming abort always cancels
• Not handling errors but expecting cancel

5. You want to cancel a fetch request if it takes longer than 3 seconds. Which code snippet correctly implements this using AbortController?

hard

A. const controller = new AbortController();
setTimeout(() => controller.abort(), 3000);
fetch(url);

B. const controller = new AbortController();
setTimeout(() => controller.abort(), 3000);
fetch(url, { signal: controller.signal })
.catch(e => console.log(e.name));

C. const controller = new AbortController();
fetch(url);
setTimeout(() => controller.abort(), 3000);

D. const controller = new AbortController();
fetch(url, { signal: controller });
setTimeout(() => controller.abort(), 3000);

Solution

1. Step 1: Setup AbortController and timeout before fetch

   Create controller, then set a timeout to call abort after 3 seconds.

2. Step 2: Pass controller.signal to fetch and handle errors

   Pass signal option to fetch and catch abort errors to avoid unhandled exceptions.

3. Final Answer:

   const controller = new AbortController(); setTimeout(() => controller.abort(), 3000); fetch(url, { signal: controller.signal }) .catch(e => console.log(e.name)); -> Option B

4. Quick Check:

   Timeout abort + signal + catch = D [OK]

Hint: Set timeout before fetch and pass signal with catch [OK]

Common Mistakes:

• Calling abort without passing signal to fetch
• Not catching abort errors
• Calling abort after fetch without signal