"Nosleep" website stops your computer falling asleep

nosleep.page does one weird trick: leave it open and it stops your computer falling asleep. This can be surprisingly annoying to accomplish through the proper channels. In my case I have a Windows laptop that can't be woken from sleep over bluetooth, but must work both as a normal sleep-when-closed laptop and as a never-sleep desktop. This solves my problem in a simple no-configuration way—the alternative is having to constantly mess with Windows' fiddly power profiles.