It spans beginner through expert in one sitting. The early questions cover things every JavaScript user meets — == vs ===, hoisting, reference vs value semantics. The later ones go into closures and this binding, the prototype chain, and the microtask/macrotask ordering behind the event loop. Your score places you in one of four tiers, and the tier names are deliberately the ones job postings use.

Neither specifically. Every question is written against core language behaviour — scope, closures, coercion, the prototype chain, the event loop — that is identical whether the code runs in a browser or in Node. Nothing here depends on a DOM API or a Node-only module.

It samples the same kind of read-and-predict reasoning most employer screens open with, in the same short-snippet format, which is why it works as preparation. It is not a copy of any specific employer test, and a good score here is not a certificate. What it does tell you is which of the four areas you would lose marks in, which is the useful thing to know before a technical interview.

About nine minutes. There is no timer on individual questions — the test measures whether you know what the code does, not how fast you can click. You can think about a question for as long as you like.