If you're prepping for a senior developer interview in 2026, you already know the landscape is brutal. LeetCode alone isn't enough anymore. Hiring managers are drilling into system design, behavioral signals, infrastructure, and how you think under pressure.
After breaking down dozens of senior-level interview loops across FAANG and high-growth startups, the same 12 topic clusters show up again and again. Here's the cheat sheet — what's actually asked, and where people get tripped up.
1. JavaScript Fundamentals That Aren't Obvious
Everyone says they know closures. Then they get asked to explain the temporal dead zone, or why typeof on an uninitialized let returns "undefined" instead of throwing.
What gets asked: the event loop (microtask vs macrotask ordering), this binding across all 4 rules, prototype chain traversal, and value-vs-reference edge cases with nested objects.
2. Async Patterns Beyond async/await
async/await is table stakes. The real questions are about Promise.allSettled vs Promise.any, cancellation patterns, and what happens when you forget a try/catch in a fire-and-forget async call (hint: unhandled rejection).
3. System Design — The Senior Separator
This is where mid-level and senior diverge. Expect to design something at scale — a URL shortener, a news feed, a rate limiter. The trap is jumping to the solution without clarifying requirements.
Framework that works: Clarify constraints → estimate scale → draw the high-level boxes → go deep on the hardest component → discuss tradeoffs explicitly.
4. Database & SQL Deep Dives
Joins everyone knows. The questions that filter people: indexing strategy (when does an index not help?), ACID isolation levels, N+1 query problems, and how to model a many-to-many with audit history.
Window functions (ROW_NUMBER, RANK, LEAD/LAG) are increasingly common in data-heavy roles.
5. Docker & Container Orchestration
"Tell me what happens when you run docker run" is a classic. Then multi-stage builds, layer caching, and why your image is 2GB when it should be 200MB.
Kubernetes questions range from basic pod/service/deployments to advanced: init containers, resource limits, rolling updates vs recreate strategy, and debugging a CrashLoopBackOff.
6. TypeScript — Where JS Devs Get Caught
Generics with constraints, conditional types, infer, and the difference between type and interface (and when it matters). The satisfies operator is a 2026 favorite.
7. Performance Optimization
Not "use a CDN" — specific optimizations. Core Web Vitals targets, code-splitting strategies, why your React re-renders too much, and how to actually measure (Lighthouse, the Performance panel, performance.mark).
8. React/Next.js Architecture
Server Components vs Client Components (the 2026 confusion point), data fetching patterns, useEffect vs event handlers, and the rendering mental model.
9. Git & Collaboration
It sounds basic, but rebase vs merge, resolving conflicts, and git reflog as your safety net come up more than you'd expect. So does: "walk me through your PR review process."
10. Behavioral — The STAR Method Actually Matters
"Tell me about a time you disagreed with a technical decision." The failure mode is being vague. Use STAR (Situation, Task, Action, Result) with quantified results. Have 5-6 stories ready that map to: conflict, failure, leadership, ambiguity, and a stretch project.
11. Cloud & Infrastructure (AWS Focus)
IAM least-privilege, VPC fundamentals, when to use Lambda vs ECS, and the cost implications of your architectural choices. "Design for failure" is the mindset they're testing.
12. Testing Philosophy
Unit vs integration vs e2e — when each matters. The testing pyramid debate, mocking strategies, and how you decide what to test. TDD comes up; have a genuine opinion.
How to Actually Prepare (Without Burning Out)
The mistake most people make: grinding 500 LeetCode problems and calling it prep. The senior loop rewards breadth + depth across these 12 areas, plus the ability to communicate clearly.
A structured approach:
- Diagnose your weak areas across the 12 topics above
- Go deep on 3-4 high-frequency topics rather than shallow on all 12
- Practice out loud — explaining system design to an empty room feels silly but works
- Build a behavioral story bank with quantified results
- Do mock interviews — even informal ones with a peer
If you want structured, topic-by-topic question banks with full answers (the kind you can review in the days before an interview), I've published a set of focused guides covering JavaScript, Python, TypeScript, SQL, Docker/Kubernetes, React/Next.js, system design, AWS, and behavioral interviews — each with 100-150 questions and worked solutions.
You can find the full set on my store: duc-store — pick the ones matching the roles you're targeting.
And if you want free, no-signup developer tools (JSON formatter, regex tester, base64, and 60+ more), I built those too: free-tools-hub.
The senior interview isn't about memorizing tricks. It's about demonstrating that you've thought deeply about the systems you build and can communicate that thinking under pressure. Pick your weak spots from the list above, go deep, and walk in confident.
Good luck out there.
What topic trips you up the most in interviews? Drop it in the comments — happy to share how I'd approach it.
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