Question 1

How do you cancel a setTimeout in JavaScript?

Accepted Answer

Store the return value (a timer ID) and pass it to clearTimeout(id). This cancels the pending timer and the callback will not run.

Question 2

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 3

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 4

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).

How do you cancel a setTimeout in JavaScript?

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