I like this solution because it's readable

The best explanation of filter I have found, online resources just werent making sense to me.

Wow u make it so smol

Super simple and clear.

The input is a list of non-negative integers and strings only. Input validation is not required then.

I think this is the closest I've come across with one exception; it doesn't check for negative numbers.

Then again, the tests don't check for it either. This is mostly a problem with the description not matching what's tested.

Not an issue

done.

That is how the stack works, last in first out. Recursion is basically doing node.concat(node.concat(node.concat..., so the inner most concat or the top of the stack executes first.

var a = 1

code golfed: function listToArray(l){return !l?[]:[l.value].concat(listToArray(l.next));}

I used recursion, but I assumed that you'd need to have a check on whethere "next" is null, but of course null is falsey, so the concat should just fail at the end. Nice, succinct.