JavaScript’s Promise.prototype.finally executes a callback when the promise is settled (resolved or rejected).
Your task is to implement a polyfill for Promise.prototype.finally.
Requirements
-
finally(callback) should run the callback once the promise settles, whether it resolves or rejects.
-
The returned promise should:
- Resolve with the original value if the promise was fulfilled.
- Reject with the original reason if the promise was rejected.
-
If the callback returns a promise, wait for it to finish before proceeding.
Example
Promise.resolve(42)
.finally(() => console.log('done'))
.then(value => console.log('resolved with', value));
// Output:
// done
// resolved with 42
Promise.reject('error')
.finally(() => console.log('cleanup'))
.catch(err => console.log('rejected with', err));
// Output:
// cleanup
// rejected with error