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Could you explain to me (s.length / 2 - 1) ? To me it is saying find the middle and move the index down one in case it is an even number string length so you can return both numbers. I don't get it, I do understand the deprication of substr and I used substring in my solution. Or if you could maybe explain what the (s.lenght / 2) - 1 means that will help as well.

A string also has a length property. Don't need to convert the string to an array with split().

substr is deprecated

Good code, but unnecessarily big.
No need to use Math.ceil (if you don't use decimal numbers) and ternary operator.
Check my solution.

Thanks! Mine was so ugly compared to this.

Great solution! This is a good way for finding the middle value for sure. I will incorporate this into my code in the future!

Clever indeed

looks cool

Because the language evolves and sometimes it's wise to stop maintaining some old features when they are replaced by newer methods, generally better. You can do easily the same thing using slice or (apparently, though I never used it) substring.