Write a polyfill for Promise.race().

Q: Write a polyfill for Promise.race().

Promise.myRace = function (promises) { return new Promise((resolve, reject) => { for (const item of promises) { Promise.resolve(item).then(resolve, reject); } }); }; const p1 = new Promise((res) => setTimeout(() => res('slow'), 100)); const p2 = new Promise((res) => setTimeout(() => res('fast'), 10)); const p3 = new Promise((res, reject) => setTimeout(() => reject('rejected firt'), 0) ); Promise.myRace([p1, p2, p3]).then(console.log).catch(console.log);

Difficulty: 5/10

Promise.race, polyfill, asynchronous control flow

resloves as soon as first promise rejects or resolves.

javascript

Scenario Questions

0-2 years experience

1How would you write a simple polyfill for Promise.race that works for an array of promises?
2What should your polyfill return if the input array is empty?
3If one of the items in the iterable isn’t a promise, how does your implementation handle it?

Follow-up Questions

What edge cases does your implementation need to consider?
How would you test it across different browsers and environments?
Can you explain how your polyfill matches the native Promise.race semantics?