Interviews for JavaScript roles focus on a small number of recurring themes. This article is the cheat sheet — what to study, what to skip, and how to talk through your answers.
The high-frequency themes
- Closures — Functions retain access to the variables of the lexical scope in which they were created — the foundation for data encapsulation and currying.
- Prototypes — Every object has an internal `[[Prototype]]` chain for property lookup.
- this binding — `this` is determined by call site: method, plain function (the global object in sloppy mode; access throws in strict mode), `new`, explicit `.
- Promises — `new Promise((resolve, reject) => .
How to structure answers
Open with the one-sentence definition. Give one real-world example. Then explain the trade-off. Interviewers score structured thinking, not encyclopedia recall — practice saying the same answer in three levels of detail.
Common follow-up traps
- "What happens when this fails?" — always have a failure mode ready.
- "How would you scale this 10x?" — show you think about the bottleneck, not just the happy path.
- "What would you change with more time?" — proves you understand the trade-offs you made.
Summary
Talk through three answers out loud today. The act of speaking forces clarity that silent reading never does.