Well, it passed the kata, so I'd say that it is a solution. With these things, all we are aiming to do is pass the tests that are given.

This is not a valid solution at all. Just execute domainName('http://mysitewww.com'). Using this solution, you will get 'mysitecom' which is absolutely incorrect. My domain is 'mysitewww'. Where is the downvote button?

Why are you using .toString()? Isn't the url given already a string?

not checking numbers in between?

Not gonna lie I love how simple this one is, its easy to understand +1

That is true. However, I was just focused on the requirements given in the kata.

This would fail with subdomains, e.g. images.google.com would return images