Web Fundamentals
Request path
DNS resolves a host; a transport connection is established; TLS authenticates and encrypts; HTTP carries requests and responses; browsers parse resources, build page structures, lay out, paint, and run scripts.
Essential concerns
- Semantic HTML and accessibility
- CSS layout, responsive design, and rendering cost
- JavaScript event loop, modules, state, and network concurrency
- HTTP methods, status codes, headers, caching, cookies, and content types
- Same-origin policy, CORS, CSP, CSRF, XSS, and secure sessions
- Progressive enhancement, loading/error/empty states, and performance budgets
Diagnostic habit
Locate the failing layer: DNS, connection/TLS, HTTP, server, data, browser policy, parsing, rendering, or application state.