JavaScript Fundamentals and Design Patterns Questions

Assess deep understanding of the JavaScript language and how to architect maintainable modular code without relying solely on frameworks. Topics include closures the prototype chain this binding scoping and the event loop including microtask and macrotask behavior. Expect questions on asynchronous patterns such as callbacks promises and async await error propagation and cancellation and on DOM event delegation and manipulation. Candidates should also explain common design patterns such as Observer Module Singleton Factory and when to apply them to build testable performant vanilla JavaScript solutions.