Part 5 · 3 chapters · ~18 min
A Question Bank Across Learna
Interview questions grouped by area, each mapped to the Learna course and part that teaches the answer: browser and JavaScript internals, React, frontend architecture, backend fundamentals, databases, distributed systems, reliability, security, money and payments, AI engineering, and leadership.
6
Frontend and runtime
| question | where it is taught |
|---|---|
| What happens between typing a URL and seeing pixels? | Browser course; Networks P7-P9 (DNS, TLS, HTTP) |
| Explain the event loop, microtasks and why await can starve rendering. | JS P10; Node P2 |
| How does React decide what to re-render, and how would you stop needless renders? | React P1-P3, P7 |
| How would you render 100,000 rows smoothly? | FSD P6; Algorithms |
| Design a design system used by 20 teams. | Design Systems; Big-company FE |
| How do hidden classes and inline caches affect performance? | JS P3-P4 |
7
Backend, data and distributed systems
| question | where it is taught |
|---|---|
| How would you guarantee a transfer is never applied twice? | API Design P8; Ledgers P3; Workflows P2 |
| Explain MVCC and why a long transaction bloats Postgres. | Postgres P3-P4 |
| When does snapshot isolation allow an anomaly? Show one. | Formal Theory P5 (write skew) |
| B-tree or LSM tree for this workload, and why? | Backend Algorithms P4; NoSQL |
| What does R + W > N buy you, and what does it not? | Formal Theory P6; Distributed Systems |
| Kafka delivered a message twice. Why, and what do you do? | Kafka; Workflows P2 |
| A service's p99 doubled after a deploy. Walk me through finding out why. | Backend Diagnosis; Systems Performance P1; SRE |
| Why does latency explode near 100% utilisation? | Statistics P8 (queueing) |
| How would you migrate a 2 TB table with no downtime? | Deploy (expand/contract); Postgres; Big-company Backend P4 |
8
Security, money, AI and leadership
| question | where it is taught |
|---|---|
| What is BOLA and how do you make it hard to write? | Backend Disciplines P1 |
| JWTs versus sessions: when each, and what goes wrong with JWTs? | Auth P1, P3 |
| Design a double-entry ledger with holds. | Ledgers P1-P2 |
| A rail call timed out. Did the money move? What does your system do? | Ledgers P4-P6; Trust course |
| How do you evaluate an LLM feature before and after a prompt change? | How LLMs Work P7; AI-native |
| Why is decoding memory-bandwidth bound? | How LLMs Work P6 |
| Tell me about a time you changed another team's direction. | this course P5; Writing P2 |
| How do you decide between building and buying? | Product Engineering; Systems Thinking |