JavaScript Interview Questions Every Developer Should Know in 2026
Closures, event loop, prototypes, async/await, and modern ES2024 features — with explanations and code samples interviewers actually ask. 1. Closures and scope. JavaScript interviews test language fundamentals, not framework trivia. These concepts appear at startups and enterprises alike — master them once and reuse across every frontend loop. 2. Event loop. A closure is a function that retains access to variables from its lexical scope even after the outer function returns. 3. Prototypal inheritance. JavaScript is single-threaded. The event loop processes the call stack, then microtasks (Promises), then macrotasks (setTimeout). Order matters in async interview questions. 4. Common coding patterns. Objects delegate to their prototype chain. Know the difference between __proto__, Object.create(), and class syntax sugar.