AbortController for cancellation in React Native

Introduction

AbortController helps you stop a task like a network request if you don't need it anymore. This saves time and device power.

When a user leaves a screen before a data fetch finishes.

When you want to cancel a slow network request to try a faster one.

When you want to stop a fetch if the app goes offline.

When you want to avoid updating the UI with old data after navigation.

Syntax

React Native

const controller = new AbortController();
fetch(url, { signal: controller.signal })
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => {
    if (error.name === 'AbortError') {
      console.log('Fetch aborted');
    } else {
      console.error('Fetch error:', error);
    }
  });

// To cancel the fetch
controller.abort();

The AbortController creates a signal to tell fetch when to stop.

Calling controller.abort() cancels the fetch and triggers an error with name AbortError.

Examples

Basic example: start fetch and cancel it later.

React Native

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

Cancel fetch automatically after 3 seconds.

React Native

const controller = new AbortController();
fetch('https://api.example.com/data', { signal: controller.signal })
  .then(res => res.json())
  .then(data => console.log(data))
  .catch(err => {
    if (err.name === 'AbortError') {
      console.log('Request was cancelled');
    }
  });

// Cancel after 3 seconds
setTimeout(() => controller.abort(), 3000);

Sample App

This React Native component fetches data when you press "Start Fetch". You can cancel the fetch anytime by pressing "Cancel Fetch". It shows loading, data, or cancellation message.

React Native

import React, { useEffect, useState, useRef } from 'react';
import { View, Text, Button } from 'react-native';

export default function FetchWithAbort() {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);
  const controllerRef = useRef(new AbortController());

  const startFetch = () => {
    setLoading(true);
    setError(null);
    setData(null);

    controllerRef.current.abort();
    controllerRef.current = new AbortController();

    fetch('https://jsonplaceholder.typicode.com/todos/1', { signal: controllerRef.current.signal })
      .then(res => res.json())
      .then(json => {
        setData(json);
        setLoading(false);
      })
      .catch(err => {
        if (err.name === 'AbortError') {
          setError('Fetch cancelled');
        } else {
          setError('Fetch error');
        }
        setLoading(false);
      });
  };

  const cancelFetch = () => {
    controllerRef.current.abort();
  };

  useEffect(() => {
    return () => {
      controllerRef.current.abort();
    };
  }, []);

  return (
    <View style={{ padding: 20 }}>
      <Button title="Start Fetch" onPress={startFetch} disabled={loading} />
      <Button title="Cancel Fetch" onPress={cancelFetch} disabled={!loading} />
      {loading && <Text>Loading...</Text>}
      {data && <Text>Title: {data.title}</Text>}
      {error && <Text>{error}</Text>}
    </View>
  );
}

Important Notes

Always handle the AbortError to avoid confusing error messages.

AbortController works only with APIs that support the signal option, like fetch.

Remember to abort fetches in useEffect cleanup to avoid memory leaks.

Summary

AbortController lets you stop fetch requests early.

Use it to save resources and improve app responsiveness.

Always handle cancellation errors to keep your app smooth.

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