AbortController for cancellation in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is AbortController used for in React Native?

AbortController helps you stop or cancel a running task, like a network request, before it finishes. It’s like pressing a stop button to save resources.

beginner

How do you create an AbortController instance?

You create it by calling new AbortController(). This gives you a controller with a signal property to pass to fetch or other cancellable tasks.

beginner

How do you cancel a fetch request using AbortController?

Call controller.abort(). This sends a signal to stop the fetch request immediately.

intermediate

What happens if you call abort() on an AbortController while a fetch is running?

The fetch promise rejects with an error named AbortError. You can catch this error to handle cancellation gracefully.

beginner

Why is it important to cancel network requests in mobile apps?

Cancelling saves battery, reduces data use, and prevents your app from doing unnecessary work when the user moves on or the screen changes.

How do you pass the AbortController signal to a fetch request?

A As the second argument in fetch options under the key 'signal'

B As the first argument to fetch

C By calling fetch.abort()

D By setting fetch.signal = controller

You pass the signal as an option: fetch(url, { signal: controller.signal })

What method do you call to cancel a fetch request?

A controller.abort()

B controller.cancel()

C fetch.cancel()

D fetch.abort()

AbortController uses the abort() method to cancel tasks.

What error name is thrown when a fetch is aborted?

A NetworkError

B FetchError

C CancelError

D AbortError

The error thrown is named AbortError.

Why should you cancel fetch requests in React Native apps?

A To speed up the app startup

B To save battery and data

C To avoid syntax errors

D To increase font size

Cancelling saves battery and data by stopping unnecessary work.

Which of these is NOT true about AbortController?

A It can cancel fetch requests

B It helps manage asynchronous tasks

C It can be reused after aborting

D It provides a signal property

Once aborted, an AbortController cannot be reused.

Explain how AbortController helps manage network requests in React Native.

Think about how you start and stop a task.

Describe why cancelling fetch requests is important in mobile app development.

Imagine your phone’s battery and data plan.

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