Node.js Event Loop: Microtasks, Timers and I/O
Reason about callback scheduling, blocking work and why timer delays are thresholds rather than guarantees.
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ENGINEERING NOTES
Engineering Notes
Practical mental models, small code examples and quick revision for backend interviews and production problem-solving. These notes explain concepts and project patterns; they do not add employment claims.
JavaScript Closures, Scope and the Temporal Dead Zone
Understand captured bindings, block scope and initialization without relying on hoisting slogans.
Async/Await and Promise.all: Concurrency and Failure
Start independent work together, handle partial failure and distinguish fail-fast from cancellation.
Limiting Async Concurrency: Workers and Backpressure
Build a bounded worker loop and understand the difference between concurrency limits, rate limits and queue capacity.
Express.js Request Lifecycle: Middleware to Error Handling
Trace a request through ordered middleware, validation, routing and a safe centralized error boundary.
REST API Architecture: Controller → Service → Repository
Place HTTP, business rules and SQL behind boundaries that support transactions and focused tests.
Authentication and Authorisation: Tokens, OIDC and RBAC
Separate identity, session renewal and resource access, including organisation-scoped authorization.
PostgreSQL for Backend Engineers: Transactions, Indexes and Pools
Connect atomic writes, query plans and pool capacity to application correctness and latency.
Redis Caching: Cache-Aside, TTL and Invalidation
Treat cached data as disposable acceleration and make stale reads, failure and invalidation policies explicit.
Idempotency and Webhooks: Duplicate-Safe Processing
Use scoped keys, authenticated webhooks and transaction boundaries to handle ambiguous delivery safely.
Transactional Outbox: Database and Message Consistency
Close the dual-write gap without pretending a database commit guarantees exactly-once message delivery.
NestJS Architecture: Modules, DI, Guards, Pipes and Interceptors
Place dependency wiring, authorization, validation and cross-cutting behavior at the right NestJS boundary.
A Practical Production Debugging Checklist
A layer-by-layer checklist for scoping incidents, verifying recovery and documenting root cause.