You could use console.log to measure whether each thing you do is having its desired effect.
There's no reason to stop at saying that the overall thing doesn't work, it is made out of smaller parts, you can test those smaller parts individually.

When posting such a question, please mention your language, post your code ( properly marked up and spoilered ), and include input and actual and expected output of a test you're failing. Help us help you!

That said, you might be forgetting a return statement.

The only way I get that error is if you have a typo in the function's name, but I've copied/pasted what you wrote there and it's ok. Click reset, and do the same I did.

It worked for me, and remember to mark your post as having spoiler content next time.

You are supposed return the answer, you're logging it in console.