const Thermostat = makeClass();
makeclass is a function
If you can include a link to the challenge that would be very helpful for anyone who wants to help you. It is impossible to know what makeClass is doing without this information – we are not sitting in front of your computer screen and cannot see what you can see.
I can guess which challenge this is, and makeClass is a function that returns a class. If you look at the challenge, it has comments saying where you need to change code. The code outside that area is for the benefit of the tests, including this function that wraps the code you’re supposed to change.