Interview question

What is the difference between Promise.all(), Promise.race(), Promise.allSettled(), and Promise.any()? Promise.all(), Promise.race(), Promise.allSettled(), और Promise.any() में क्या अंतर है?

Answer

Method	Resolves when	Rejects when
Promise.all()	All promises fulfill	Any one rejects (fails fast)
Promise.race()	First promise settles (fulfilled or rejected)	First settled is a rejection
Promise.allSettled()	All promises settle, regardless of outcome	Never rejects
Promise.any()	First promise fulfills	All promises reject

const p1 = Promise.resolve(1);
const p2 = new Promise(res => setTimeout(() => res(2), 100));
const p3 = Promise.reject('error');

// Promise.all - fails fast on first rejection
Promise.all([p1, p2])
    .then(results => console.log(results)); // [1, 2]
Promise.all([p1, p3])
    .catch(err => console.log('Failed:', err)); // Failed: error

// Promise.race - first to settle wins
Promise.race([p1, p2])
    .then(result => console.log('First:', result)); // First: 1

// Promise.allSettled - always resolves with status of each
Promise.allSettled([p1, p3]).then(results => {
    console.log(results);
    // [{status:'fulfilled', value:1}, {status:'rejected', reason:'error'}]
});

// Promise.any - first fulfillment, ignores rejections unless all fail
Promise.any([p3, p2])
    .then(result => console.log('First success:', result)); // First success: 2

// Practical use case - fetch data from multiple APIs concurrently
async function loadDashboard() {
    const [users, orders, stats] = await Promise.all([
        fetch('/api/users').then(r => r.json()),
        fetch('/api/orders').then(r => r.json()),
        fetch('/api/stats').then(r => r.json())
    ]);
    return { users, orders, stats };
}

Method	कब resolve होता है	कब reject होता है
Promise.all()	सभी promises fulfill हों	कोई एक reject हो
Promise.race()	पहला promise settle हो	पहला settled reject हो
Promise.allSettled()	सभी settle हों	कभी reject नहीं होता
Promise.any()	पहला fulfill हो	सभी reject हों

const p1 = Promise.resolve(1);
const p2 = new Promise(res => setTimeout(() => res(2), 100));
const p3 = Promise.reject('error');

// Promise.all - पहली rejection पर fail
Promise.all([p1, p2]).then(results => console.log(results)); // [1, 2]

// Promise.race - पहला settle जीतता है
Promise.race([p1, p2]).then(result => console.log('First:', result)); // 1

// Promise.allSettled
Promise.allSettled([p1, p3]).then(results => console.log(results));

// Promise.any
Promise.any([p3, p2]).then(result => console.log('Success:', result)); // 2

// Multiple APIs एक साथ
async function loadDashboard() {
    const [users, orders] = await Promise.all([
        fetch('/api/users').then(r => r.json()),
        fetch('/api/orders').then(r => r.json())
    ]);
    return { users, orders };
}

Was this answer clear?

Subjects

Related questions