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In modern times that's something you can easily throw far back in mindbank, because in practice using ES6 it almost never comes up, and it's super easy to do a quick refresher on the semantics. If I didn't know that interviewers tended to ask about it in frontend inteviews (because they totally do), would never bother to keep up to date with the semantics

Object.defineProperty('senior', { value: true, enumerable: false })

There are two things I would expect even a mid level developer to know - how prototypical inheritance works and how “this” works in JS.