Mutating an argument is the worst thing you can do.

This is what I did. Awesome job!

you can do this if you have exactly one parameter.

cool , I did this the same way but put the 'list' parameter into parenthesis,dindn't know I could do it without it.

Yes, I would very much like to know the difference as well... Have you tried stackoverflow @vlakas

You deleted the Python examples which need to be restored. The description is shared between all languages. In order to show descriptions for multiple languages you just stack them next to each other, the system will filter out the ones that are not relevant to the language being trained on.

circleArea("1") should return false as "If the radius is not positive or not a number, return false.", but it returns 3.14.

toFixed does round.

The "Boolean primitive" is a boolean. ToNumber is well defined on booleans. And isNaN works in terms of ToNumber.

That being said, the kata is underspecified at that point, as it isn't clear if the type of the argument should be checked. After all, it says only that "[i]f the radius is [...] not a number, return false". And that can be easily interpreted as isNaN returns true. The the abstract relational comparison algorithm makes sure that the inintial comparison is true if and only if radius was actually a number (or convertable with ToNumber).

The solution provided by ColbyDauph et al is therefore perfectly valid for any input, as long as you concur with the definition of "number" given above. If you object that defintiion, suggest a kata edit to clear that issue.

Passing true to the function should result in false (as the the Boolean primitive is NaN), however the result returned is 3.14

Sometimes unknown error occured

Tests are failing