Questions

10 of 17

1Explain the concept of 'callback hell' and how to mitigate it.

2What is a Promise in JavaScript?

3Explain the three states of a Promise.

4How do you create a new Promise in JavaScript?

5What is the purpose of `Promise.resolve()` and `Promise.reject()`?

6How do you handle the result of a Promise?

7What is Promise chaining?

8How do you handle errors in a chain of Promises?

9What is the purpose of `Promise.all()`, `Promise.race()`, `Promise.any()`, `Promise.allSettled()`?

10How can you handle multiple Promises concurrently without using `Promise.all()`?

11What is the purpose of the `async` and `await` keyword in JavaScript??

12How do you handle errors when using `async/await`?

13Do all `async` functions return Promises? Why or why not?

14How does `Promise.finally()` work?

15How do you convert a callback-based function into a Promise-based function?

16What is the purpose of `Promise.promisify()`?

17How can you create a custom Promise with timeout functionality?

10 / 17

How can you handle multiple Promises concurrently without using `Promise.all()`?

Difficulty: 5/10

You can either chose in built methods like allsettled(), race(), any().

1
Promise.race(): The first resolved Promise (or the first rejected one) will determine the outcome.
2
promise.allSettled : Fulfills when all promises settle.
3
promise.any(). Fulfils when any of the promises are fulfilled; rejects when all of the promises are rejected.

Manual async/await Triggering (Array.map) By initiating all promises before awaiting them, they execute concurrently in the background. You can then await them individually using Array.map() inside Promise.allSettled or a custom tracking loop.

Custom Concurrency Manager (Semaphore / Pool) When handling dozens or hundreds of requests, running everything in parallel can exhaust memory or hit API rate limits. You can control maximum concurrency using an async pool pattern:

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