Promise chaining in Javascript - 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 you return a new promise inside a .then() callback?

The next .then() waits for that new promise to resolve before running, allowing you to chain asynchronous operations smoothly.

beginner

How do you handle errors in a promise chain?

You can add a .catch() at the end of the chain to catch any error from any promise in the chain.

beginner

What is the benefit of promise chaining over nested callbacks?

Promise chaining avoids deeply nested code (callback hell), making asynchronous code easier to read and maintain.

What does promise.then() return?

A Undefined

B The resolved value immediately

C The original promise

D A new promise

then() always returns a new promise that resolves with the value returned inside its callback.

How can you pass data from one promise to the next in a chain?

A By using global variables

B By returning the data inside <code>.then()</code>

C By calling <code>resolve()</code> manually

D By using <code>setTimeout()</code>

Returning data inside .then() passes it to the next .then() callback.

What happens if a promise in the chain rejects and there is no .catch()?

A The chain stops and error is unhandled

B The error is ignored

C The next <code>.then()</code> runs anyway

D The promise resolves with undefined

Without .catch(), a rejection causes an unhandled promise rejection error and stops the chain.

Which of these is a correct way to chain promises?

A promise.then(() => promise2).then(() => promise3)

B promise.then(promise2).then(promise3)

C promise.then(() => promise2.then(() => promise3))

D promise.then(() => promise2).then(promise3())

Returning a promise inside .then() correctly chains the promises.

Why is promise chaining preferred over nested callbacks?

A It uses less memory

B It runs faster

C It makes code shorter and easier to read

D It avoids using functions

Promise chaining avoids nested code, making asynchronous flows clearer and easier to maintain.

Explain how promise chaining works and why it is useful.

Think about how you can do one task after another without nesting functions.

Describe how errors are handled in a promise chain.

Consider what happens if something goes wrong in any step.