For anyone wondering, this is definitely and absolutely NOT best practice! Its not even a clever solution.

oh nice code

i suppose the solution must be more native and contain basic language feature.))

I thought the 0 was for if the array was empty.

?= is a lookahead assertion. It checks for the match (with any uppercase letter in this case: [A-Z]) but doesn't include it in the match.

Can somebody explain this /(?=[A-Z])/?

Great one-liner. This solution has a space complexity of O(n) because an array is allocated. In place sorting solutions can have a space completity of O(1).

That was my first solution, but it does not consider input validation according to description:
"... accepts a string containing up to 26 unique alphabetical characters."

I remember what functions exist in many languages, then do a search to find out what that particular language calls them. Most languages have a similar set of basic functions (except those languages that don't support higher-order functions cough), and that set really isn't very big. Most of what ZozoFouchtra lists exist under some alias in all languages that can handle them. For example, I may search for “js fold” (knowing foldl and foldr from Haskell), which takes me directly to MDN's page about Array.prototype.reduce(). I don't use JS much, but when I do, this is my workflow.

.forEach(), .every(), .filter(), .map(), .reduce() and .reduceRight() are (useful) methods of Array since JavaScript 1.6.
You'll find many occasions to use them in Codewars. ;)

see more @ https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

How do you people come up with such answers ? do you google inbetween or you just know all the functions ?

why did you use regxp to evaluate, simple > would be more elegant!

Its grate, but this is not correct solution, instructions where rather clear you shuld accept max 26 caracters. N

"I have developed an elegant solution to this problem."

1 minute later. . .

"Oh, there was already a method for that."