AbortController for cancellation in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when an AbortController aborts a fetch?

Consider this Node.js code using AbortController to cancel a fetch request. What is the output or behavior when the controller aborts the fetch?

Node.js

import fetch from 'node-fetch';
const controller = new AbortController();
const signal = controller.signal;

fetch('https://httpbin.org/delay/5', { signal })
  .then(() => console.log('Fetch succeeded'))
  .catch(err => console.log(err.name));

setTimeout(() => controller.abort(), 1000);

A Logs 'AbortError' after about 1 second

B Logs 'Fetch succeeded' after 5 seconds

C Throws a SyntaxError immediately

D Logs 'TypeError' after 1 second

💡 Hint

Think about what happens when the abort signal triggers during a fetch.

When the AbortController aborts, the fetch promise rejects with an error named 'AbortError'. This happens shortly after abort() is called, not after the full delay.

📝 Syntax

intermediate

Which option correctly creates an AbortController and uses its signal in fetch?

Select the code snippet that correctly creates an AbortController and passes its signal to fetch in Node.js.

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

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

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

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

💡 Hint

Remember how to instantiate classes and what fetch expects for the signal option.

Option B correctly creates an AbortController instance and passes its signal property to fetch. Option B misses 'new', C passes the controller itself instead of its signal, and D also passes the controller instead of the signal.

🔧 Debug

advanced

Why does this fetch never abort despite calling controller.abort()?

Look at this code snippet. The fetch request never aborts even though controller.abort() is called. What is the reason?

Node.js

import fetch from 'node-fetch';
const controller = new AbortController();

fetch('https://httpbin.org/delay/5')
  .then(() => console.log('Done'))
  .catch(err => console.log(err.name));

setTimeout(() => controller.abort(), 1000);

A The fetch call does not use the controller.signal, so abort has no effect

B AbortController is not supported in Node.js

C controller.abort() is called too late to affect fetch

D fetch automatically ignores abort signals

💡 Hint

Check if the fetch call is connected to the AbortController signal.

The fetch call must receive the signal option from the AbortController to be abortable. Here, fetch is called without the signal, so aborting the controller does nothing.

❓ state_output

advanced

What is the state of AbortController.signal.aborted after calling abort()?

Given this code, what is the value of signal.aborted after controller.abort() is called?

Node.js

const controller = new AbortController();
const signal = controller.signal;
console.log(signal.aborted);
controller.abort();
console.log(signal.aborted);

A true then true

B true then false

C false then false

D false then true

💡 Hint

Check the initial and post-abort values of the aborted property.

Initially, signal.aborted is false. After calling controller.abort(), it becomes true indicating the signal is aborted.

🧠 Conceptual

expert

Why use AbortController with fetch in Node.js?

Which is the main reason to use AbortController with fetch in Node.js?

A To convert fetch responses into streams

B To automatically retry failed fetch requests

C To cancel an ongoing fetch request to save resources or respond to user actions

D To increase fetch request timeout beyond default limits

💡 Hint

Think about what aborting a fetch achieves.

AbortController allows canceling a fetch request before it completes, useful for stopping slow or unwanted requests, saving bandwidth and CPU.