These kinds of questions are very different from questions about browser quirks. These questions get at the depth of understanding of the language itself. It is akin to understanding how a C++ program is going to use the stack and the heap, etc. Only after understanding the language fundamentals can you answer these questions and only then can you truly understand the code you are writing. With depth of understanding comes an ability to make better decisions about how and when to use and tool. Almost anyone can use jQuery, but writing it or something like it requires a different level of knowledge.