JAVASCRIPT GUIDE
JavaScript Closures Explained for Interviews
By the HireReadyAI team · 8 min read
What closures are, why they matter in callbacks and React, and common stale-closure bugs.
What a closure is
A closure is when a function remembers the variables from the scope where it was created, even after that outer function has returned. This is ordinary JavaScript — callbacks, event handlers, and hooks all rely on it.
Why it matters
Closures enable data privacy patterns, partial application, and stateful callbacks. In React, effects and handlers close over props and state — stale closures are a common bug when dependencies are wrong.
Pitfalls
Classic loop-with-var bugs, retaining large objects longer than expected (memory), and stale values in async callbacks. Prefer let/const, copy values you need, and understand dependency arrays in UI frameworks.
Interview answer
Define closure, give a small code example, then mention one real bug (stale state) and how you prevent it. That beats a memorized textbook sentence.