Code accepted by Codecademy and still it gives an Error message (bottom of screen shot)

link
This code works in Firefox console
const isEven = num => (num % 2) === 0 ? 'true' : 'false';
but the Codecademy IDE says that 'isEven(0)` should return true. In the web console it returns true.

You’re returning a string. From the description I understand that you should return a boolean.

I see. Pesky little single quotes…
Thank you.