Promises for cleaner async in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Promise in JavaScript?

A Promise is an object that represents the eventual completion or failure of an asynchronous operation. It helps write cleaner code by avoiding deeply nested callbacks.

beginner

What are the three states of a Promise?

A Promise can be in one of three states: pending (initial state), fulfilled (operation completed successfully), or rejected (operation failed).

beginner

How does the then() method work with Promises?

The then() method is used to specify what to do when a Promise is fulfilled. It takes a callback function that runs with the resolved value.

beginner

What is the purpose of the catch() method in Promises?

The catch() method handles errors or rejections from a Promise. It runs a callback if the Promise is rejected, helping to manage failures cleanly.

intermediate

How do Promises help make asynchronous code cleaner compared to callbacks?

Promises avoid "callback hell" by chaining then() calls instead of nesting callbacks. This makes the code easier to read and maintain.

Which Promise state means the operation is still running?

A Rejected

B Pending

C Fulfilled

D Resolved

A Promise is 'pending' while the asynchronous operation is still in progress.

Which method is used to handle a successful Promise result?

A then()

B catch()

C finally()

D resolve()

The then() method runs a callback when the Promise is fulfilled successfully.

What does the catch() method do in a Promise chain?

A Returns the Promise value

B Starts the Promise

C Handles errors or rejections

D Cancels the Promise

catch() handles errors or rejected Promises to keep code clean and avoid crashes.

Which of these is NOT a Promise state?

A Resolved

B Rejected

C Fulfilled

D Pending

'Resolved' is not an official Promise state; the correct states are pending, fulfilled, and rejected.

Why are Promises preferred over nested callbacks?

A They run faster

B They avoid using functions

C They use less memory

D They make code easier to read and maintain

Promises allow chaining which avoids deeply nested callbacks, making code cleaner and easier to follow.

Explain how Promises improve asynchronous code compared to callbacks.

Think about how you handle success and errors without nesting functions inside each other.

Describe the lifecycle of a Promise from creation to completion.

Imagine waiting for a package delivery: waiting, delivered, or failed.