This is clever but not best practice. Only code that is clear should be allowed to be considered best practice.

Can you explain what "array size extension" is exactly? I'm looking at your answer and see "fill" and "concat". Would these not be considered array size extensions also? Is your answer the best answer? If so, is filling a new array and concat better than push and spreading? How come?

It's clever for sure. But usually clever != best practice.

I'm familiar (not expert) with regular explressions and this is hard to read.

You could say "get familiar with X concept and then it will be easy" for anything that is considered hard for the average person.

Best practice means best for the average person.

Hard to read code is not best practice.

2 loops unnecessarily is not best practice.

The description was harder than the actual problem.
The description should be rewritten to be clear.

Exactly. This kata is too advanced for 6 kyu.

This is why this kata should be lower than 6 kyu. Performance and optimization is advanced stuff.

It would be easy if performance wasn't a factor. But knowing about best performing loops and alogorithms certainly is too difficult for 6 kyu.

How is it not a string? When doing "typeof title" it says "string". What am I missing?

I had the same problem. Is it reallly a problem with our code or with the way codewars keeps track of global variables?

I guess you have to be clever to pass the tests without solving the problem.

These math problems, as opposed to programming problems which is the reason people come here, give the wrong impression that programming requires good math knowledge, while in practice it's not like that.