Move beyond Jest mocks. Use Vitest for ESM support and speed, TestContainers for real databases, MSW for HTTP mocking, and contract testing with Pact for production confidence.
Master Worker Threads for CPU-bound tasks. Learn MessagePort communication, SharedArrayBuffer optimization, and building production-ready worker pools with real image processing examples.
Master PKCE (Proof Key for Public Clients) for JavaScript SPAs and mobile apps. Learn code verifier generation, state parameters, token storage, refresh flows, and scope design.
Implement the three pillars: Prometheus metrics, Loki structured logging, and Tempo distributed tracing. Correlate with trace IDs for complete request visibility.