clever

It seems that performance leaks are not issue for this purpose as any roman number can't extremelly big in reality. Cool approach, especially for fromRoman function. Unfortunatelly substr is already considered as deprecated, so it may be replaced

pretty clever, well done!.. my refactored solution has a slightly better performance since it doesn't use nested loops.

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?

looks like it is a performance heavy solution

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sometimes there is www1 , www2 ... but other than that , the code is good and elegant

Some sample test cases are wrong