Twenty-five multiple-choice questions, one from each lesson of JavaScript Under the Hood. Every one puts real code in front of you and asks what it does: what the engine has in memory before the first line runs, why a loop with var prints 6 five times, which queue drains first, what a const object will and will not let you change. This is not a syntax quiz. There is nothing here about which method appends to an array. The questions are about the model underneath, which is what breaks in real code and what interviews are actually probing. Every question carries a code snippet. Six are straightforward, twelve take a minute of tracing, and seven are hard. Every learner sits the same twenty-five questions, so one score can be compared with another.

Developers who write JavaScript daily and want to know whether they understand it or have just memorised what usually works. It is also close to what a mid-level JavaScript interview asks. It assumes you can read a function, an arrow, and an array method without looking them up. It does not assume you have read the specification, and it does not test framework knowledge.