Promise catch for async errors in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the catch method do in a Promise?

The catch method handles errors or rejections that happen in the Promise chain. It lets you respond to problems without crashing your program.

beginner

How do you attach a catch to an async function call that returns a Promise?

You call the async function and then add .catch(error => { /* handle error */ }) after it to catch any errors that happen inside the async function.

beginner

Why is it important to use catch with Promises?

Without catch, errors inside Promises can go unnoticed and cause your app to behave unexpectedly or crash. catch helps keep your app stable by handling those errors.

intermediate

What happens if you forget to add catch to a Promise?

If you forget catch, unhandled Promise rejections may occur, which can cause warnings or crashes depending on your Node.js version and settings.

beginner

Show a simple example of using catch with an async function.

Example:<br><pre>async function fetchData() {
  throw new Error('Oops!');
}

fetchData()
  .catch(error =&gt; console.log('Error caught:', error.message));</pre>

What does promise.catch() do?

A Handles errors from the Promise

B Starts a new Promise

C Resolves the Promise successfully

D Cancels the Promise

catch is used to handle errors or rejections from a Promise.

Which of these is the correct way to catch errors from an async function getData()?

A getData().catch(error => console.log(error))

B catch(getData())

C getData().then(error => console.log(error))

D getData().error()

You attach .catch() directly to the Promise returned by the async function.

What happens if you don't use catch on a Promise that rejects?

A The Promise retries automatically

B The error is ignored silently

C The Promise resolves anyway

D Node.js may show an unhandled rejection warning or crash

Unhandled Promise rejections can cause warnings or crashes in Node.js.

Can catch be used to handle errors from multiple Promises chained together?

A No, each Promise needs its own catch

B Yes, one catch at the end can handle errors from the whole chain

C Only if Promises are run in parallel

D Only if Promises are synchronous

A single catch at the end of a Promise chain catches errors from any Promise in the chain.

Which Node.js version introduced warnings for unhandled Promise rejections by default?

A Node.js 6

B Node.js 8

C Node.js 10

D Node.js 12

Node.js 10 started showing warnings for unhandled Promise rejections by default.

Explain how to use catch to handle errors from an async function returning a Promise.

Think about how you would stop your app from crashing when an async call fails.

Why is it important to always add a catch when working with Promises in Node.js?

Consider what happens if errors are ignored in your code.