done.

Thank you for these comments! Your reply and solution helped me think about this problem in a completely different way.

'filter' creates a new array + iterates through the total array.
the 'reduce' solution stops when needed and returns a boolean.

Need to improve on instructions text

doesnt this throw error for numbers as params?
Example: greetingForAllFriends(34);

I agree. changing prototype is not a good practise. But using filter method is good.

It looks like your solution might be better :) Did you test its performance somehow? What do you mean by "most efficient in terms of space"?

duuhh! Thanks!

toString() is not required :)

I think I struck a good balance. For more complex solutions, I usually add comments to help new-comers, but this kata was simple enough I didn't think it necessary.

The regex flag, 'i', might not be needed.
But the question doesnt explicitly say that it needs case sensitive comparison, although the tests pass without the flag, 'i'.