Promise chaining in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is promise chaining in JavaScript?

Promise chaining is a way to run multiple asynchronous tasks one after another, where each task starts when the previous one finishes, using .then() methods.

beginner

How do you return a value from one promise to the next in a chain?

You return the value inside the .then() callback. This value becomes the input for the next .then() in the chain.

intermediate

What happens if a promise in the chain is rejected?

If a promise is rejected, the chain skips to the nearest .catch() handler to handle the error.

beginner

Why is promise chaining better than nested callbacks?

Promise chaining avoids deeply nested code (callback hell), making code easier to read and maintain by keeping asynchronous steps in a flat, linear structure.

beginner

Show a simple example of promise chaining with two asynchronous steps.

Example:

fetchData()
  .then(data => processData(data))
  .then(result => console.log(result))
  .catch(error => console.error(error));

This runs fetchData, then processData with the fetched data, then logs the result, handling errors if any.

What method do you use to add the next step in a promise chain?

A .then()

B .catch()

C .finally()

D .start()

The .then() method adds the next step to a promise chain.

If a promise in the chain fails, which method handles the error?

A .then()

B .finally()

C .error()

D .catch()

The .catch() method handles errors in promise chains.

What does returning a promise inside a .then() do?

A Ends the chain

B Waits for that promise before continuing the chain

C Starts a new unrelated chain

D Ignores the returned promise

Returning a promise inside .then() makes the chain wait for it to resolve before moving on.

Which problem does promise chaining help to solve?

A Callback hell

B Memory leaks

C Synchronous blocking

D Variable hoisting

Promise chaining helps avoid deeply nested callbacks known as callback hell.

What will this code output?

Promise.resolve(5)
  .then(x => x * 2)
  .then(x => x + 1)
  .then(console.log);

A 5

B 10

C 11

D Error

The chain multiplies 5 by 2 (10), then adds 1 (11), then logs 11.

Explain how promise chaining works and why it is useful.

Think about how you do tasks one after another and how promises help with that.

Write a simple promise chain that fetches data, processes it, and logs the result, including error handling.

Start with a promise, then add steps with .then(), and end with .catch()