The main problem with your response is that the threshold for "basic concept" is arbitrary by framework, by language, by time, by interviewer. Revert back to interviewing things relevant for the day to day job, look at what developers actually employed there did over the last few weeks, and interview on that.
Asking about async/sync in JS is completely different from asking someone what obscure features like finalizers are in Java. One is used on an hourly basis when writing code, the other one is never used except in obscure legacy code.
If you do what you're proposing and just ask about projects I think you'll find it's easy for incompetent people who are floundering around and copy pasting from stackoverflow without understanding what they're copying to pass your bar. I copy from stack overflow all the time but I understand what I'm copying and why it works and when it doesn't work.
`async` questions are the most day job relevant questions I can imagine for a javascript developer. It is so pervasive, a such a simple piece of syntactic sugar over basic asynchronicity, that not knowing it is damning along a number of axes.