Question 1

What is the output of Promise.resolve(1).catch(e => 'catch').then(n => console.log(n))?

Accepted Answer

then 1. .catch only runs on rejection. Since the promise is fulfilled (resolve(1)), .catch is skipped, and .then receives 1.

Question 2

What is the output of Promise.resolve(1).then(n => { n + 1; }).then(n => console.log(n))?

Accepted Answer

undefined. The first .then has a block body (braces) with no return statement. Block bodies need an explicit return. Without it, the function returns undefined, and the next .then receives undefined.

Question 3

Does .catch run on a fulfilled promise in JavaScript?

Accepted Answer

No. .catch only runs on rejection or when a .then above it throws. If the promise is fulfilled, .catch is skipped and the next .then receives the value.

Question 4

What happens after .catch in a promise chain in JavaScript?

Accepted Answer

The chain continues as fulfilled with the value returned by .catch. If .catch returns 'recovered', the next .then receives 'recovered'. If .catch re-throws, the next .catch catches it.

What is the output of Promise.resolve(1).catch(e => 'catch').then(n => console.log(n))?

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