i absolutely hate how the modern web just fails to load if one has javascript turned off. i, as a user, should be able to switch off javascript and have the site work exactly as it does with javascript turned on. it’s not a hard concept, people.
but you ask candidates to explain “graceful degradation” and they’ll sit and look at you with a blank stare.
A button to toggle is good design, but it should just default to your system preferences.