From foundations to staff-level.

The language and the platform. JavaScript core, the DOM, and how the browser actually renders. Every interview at every level builds on this floor.

Async JavaScript, React fundamentals, and the daily UI surfaces — forms, lists, networking. The bar for mid-level coding rounds at most product companies.

How React actually works under the hood, performance engineering, testing strategy, and the security posture interviewers expect you to bring up unprompted.

Frontend architecture, build tooling, and component-level system design. The point where interviews stop being about syntax and start being about tradeoffs.

Multi-team frontend system design, platform thinking, and the cross-cutting concerns — observability, rollout safety, design systems at scale — that staff loops drill into.