Question 1

What is the output of console.log('1'); setTimeout(() => console.log('2'), 0); console.log('3') in JavaScript?

Accepted Answer

1, 3, 2. The timer callback goes to the macrotask queue and runs after the synchronous code finishes.

Question 2

Why does a Promise callback run before a setTimeout callback in JavaScript?

Accepted Answer

Because promise callbacks go to the microtask queue, which the event loop drains completely before touching the macrotask queue where setTimeout callbacks live.

Question 3

What is the output of for (var i = 0; i < 3; i++) setTimeout(() => console.log(i), 0) in JavaScript?

Accepted Answer

3, 3, 3. var is function-scoped; all callbacks share one i, which is 3 by the time they run. Use let to fix this (logs 0, 1, 2).

Question 4

Can a setTimeout callback run before the specified delay in JavaScript?

Accepted Answer

No. The callback never runs before the delay. It may run later (if the call stack is busy or microtasks are queued), but never earlier than the delay.

What is the output of console.log('1'); setTimeout(() => console.log('2'), 0); console.log('3') in JavaScript?

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