#428 Retry Promises N Times

Implement a function retryPromise that retries executing a promise-returning function up to n times if it fails.

Requirements

• Input is a function fn that returns a promise, and an integer n (maximum retry attempts).
• If fn resolves at any attempt, return its resolved value immediately.
• If all attempts fail, reject with the last error.
• Each retry should only be triggered when the previous attempt fails.
• The function should work even if n = 0 (i.e., try only once).

Example

let count = 0;
const unreliable = () => {
  count++;
  return count < 3
    ? Promise.reject('fail')
    : Promise.resolve('success');
};

retryPromise(unreliable, 5).then(console.log).catch(console.error);
// Output: "success"

retryPromise(() => Promise.reject('always fails'), 2)
  .then(console.log)
  .catch(console.error);
// Output: "always fails"

Constraints

• fn is always a function that returns a promise.
• n is a non-negative integer.
• Must reject immediately if the final attempt fails.