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Javascript Interview: 5 promise questions you can see in your interview

Eishta Mittal
Towards Dev
Published in
3 min readJan 6, 2025

1. Guess the output

new Promise((resolve, reject) => {
resolve(1)
resolve(2)
reject('error')
}).then((value) => {
console.log(value)
}, (error) => {
console.log('error')
})

Answer: 1

Explaination:

When the new promise is created, it is immediately resolved with the value 1 in the first resolve(1) statement. Although resolve(2) and reject('error') are called afterward, they are ignored because a promise can only be settled once. Since the promise resolves with 1, the .then() method's success callback is triggered, logging 1. The rejection callback (error) is never called, as the promise was already resolved.

2. Guess the output


console.log(1)
const promise = new Promise((resolve) => {
console.log(2)
resolve()
console.log(3)
})

console.log(4)

promise.then(() => {
console.log(5)
}).then(() => {
console.log(6)
})

console.log(7)

setTimeout(() => {
console.log(8)
}, 10)

setTimeout(() => {
console.log(9)
}, 0)

Answer: 1 2 3 4 7 5 6 9 8

Explaination:

  1. console.log(1) prints 1.
  2. The promise constructor runs, logging 2, then resolves, logging 3.

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Published in Towards Dev

A publication for sharing projects, ideas, codes, and new theories.

Written by Eishta Mittal

Software Engineer passionate about Frontend Engineering

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