Did you evaluate the asymptotic complexity of the algorithm? It is probably O(n log(n)), where n is the number of digits of the number (you need n steps to find the first digit to swap, and then you want to sort the digits on the right). I guess hard numbers are hard only if the algorithm is wrong, but I see a lot of people whose program times out so I guess they already trip in bad cases...

Not an issue. Your logs appear before the test-result message.

A test case is wrong in JavaScript, with base 10 and exp 10000000000 as arguments, and returning 0 as final digit, I'm getting an error with message: 'Expected: 9, instead got: 1'

Why do you say so? It has indeed its logic, otherwise how could it be completed more than 12k times?

Not an issue, neither of those is the input, print it if you want to know what is was.

This solution just cant handle 93394999987652