Question 1

What happens if a .then callback throws an error in JavaScript?

Accepted Answer

The error propagates to the next .catch in the chain. Subsequent .then callbacks are skipped. If there is no .catch, it becomes an unhandled rejection.

Question 2

What is the output of console.log('1'); Promise.resolve().then(() => console.log('2')); console.log('3')?

Accepted Answer

1, 3, 2. The .then callback is a microtask; it runs after the synchronous code (1 and 3) completes and the call stack is empty.

Question 3

Does .catch run on a fulfilled promise in JavaScript?

Accepted Answer

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

Question 4

What is the difference between Promise.all and Promise.allSettled in JavaScript?

Accepted Answer

Promise.all rejects if any promise rejects (fast fail). Promise.allSettled waits for all promises, even if some reject, and returns an array of { status, value/reason } objects.

What happens if a .then callback throws an error in JavaScript?

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