GitHub Pages can't run Node.js — so this page implements an Express-like server framework in pure JavaScript, complete with routing, middleware chain, authentication, rate limiting, and structured error handling. Every request you make below is processed through a real middleware pipeline, right here in the browser.
This isn't a mock. The code on the left is a functioning server framework — a simplified
Express.js reimplementation running in the browser. Every middleware function executes in sequence,
each calling next() to pass control forward. The pipeline visualizer shows real timing data
from each step.
The concepts demonstrated: route matching with parameter extraction, middleware composition, bearer token authentication, request rate limiting with a sliding window, input validation, structured JSON error responses with proper HTTP status codes, CORS headers, and content-type negotiation.
On a real server this exact pattern runs on Node.js with Express, Fastify, or Koa. The middleware chain, route matching logic, and error handling patterns are identical — the only difference is the transport layer (HTTP sockets vs. in-memory function calls).