Execution Contexts, Closures, and Object Prototypes

The difference between a mid-level and senior frontend engineer often reveals itself the moment an interviewer asks about execution contexts, dynamic `this` resolution, or prototype chain delegation. Rather than relying on memorized rules, candidates must reason about how the JavaScript engine allocates Lexical Environments during function creation and invocation.

Here, you will visualize the mechanics of closures retaining outer variables, step through the 4 rules of `this` binding at call-sites, and trace prototype lookups directly to null. These concepts are directly applicable to building resilient, bug-free components.