For "real world use", I think a string without an hash should be tested as well:
check('www.codewars.com', 'www.codewars.com')

You are supposed to write yourself all the solutions

It has nothing to do with having to write everything from scratch.

ROTFL!

Crazy initialization by 9007199254740992 ... 😆

1. instead of val += you could also write val = val + ...
2. You asked about val += val. The second val doesn't belong to the first one. It belongs to the comparison val > 1.

I usually use brackets for better readability:

val += (val > 1) ? ' ' + key + 's' : ' ' + key

If you use a template string, you could write it like so:

val = `${val} ${key}${(val > 1) ? 's' : ''}`

Hope I didn't code it wrong ;)

I like this solution. Few and performant code! Well done.

I like it.
Nevertheless one should notice that substr() is marked as deprecated:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr