Web Development Intermediate

HTTP, browsers, servers, DNS, and the request-response cycle that powers every web page.

How HTML provides structure, CSS provides presentation, and JavaScript provides behavior in every web page.

Visual map of how a browser request travels from URL to rendered page through DNS, TCP, TLS, HTTP, and rendering stages.

Resource-oriented design, HTTP methods and status codes, idempotism, versioning, pagination, and error response patterns.

Client-side state with React/useState, server state with sessions and JWT, cookies vs localStorage, and caching strategies.

An API contract defines the meaning of operations, inputs, outputs, errors, and side effects.

Follow a POST request from key validation through durable result storage so a lost response does not create a second resource.

See how authentication, key lookup, atomic work, stored outcomes, and retry replay prevent duplicate create operations.

Track the last accepted timestamp for each message and reason about state growth, ordering, and concurrent requests.

A backend prompt about uncertain outcomes, idempotency keys, atomic state changes, timeouts, and downstream side effects.

A planned scenario shows how a lost response creates uncertainty and how idempotency keys define one logical operation.