Yours is a very skillful solution indeed. Thanks for explaining its implementation.

You might want to change the description to say "6 character string" instead of "6 digit string" since strings are not restricted to digits only. Also, maybe change examples of using photoManager.nameExists() so they're called with a 6 character long argument.

I don't think your solution is actually passing all the tests. Rather, an error is being thrown that stops further tests from being run. Consider what String.prototype.match returns if there are no matches.

I tried re-wording your description text to make it more clear and improve the grammar a bit:

Given a string, return the letter that appears most frequently. If multiple letters appear with the maximum frequency, return the letter that appears earliest in the alphabet. If the string has no letters, return null. Treat letters as case-sensitive.

/* issue irrelevant to updated kata */

A couple typos here. "help adjust it's difficulty" & "consensus on it's ranking" should use "its" not "it's".

Also, "Codewars users with over 50 Honor, earn the privilege" shouldn't have a comma. The same probably goes for "an additional +2 Honor per kata, for contributing".

Typo in description: 'Saggitarius' should be 'Sagittarius'.

It's definitely 'asterisk' in English. OED says it's from the Greek 'asteriskos' meaning 'small star'.

Definitely worth disabling native array methods to force the kind of solution you're looking for.

Could also remove the comments pointing out where code should be written.