Build Your Own

You understand a system properly once you have built a small one that works. Every module here is a real, tested implementation you can run, read in an evening, and break on purpose: a Redis that speaks the real protocol to redis-cli, a Kafka with segment files and consumer groups, a compiler down to bytecode and a VM, a transpiler that emits source maps a browser debugger follows, two frameworks (one built on signals, one built on React's fiber model), a bundler that tree-shakes and code-splits, a kernel that schedules and pages, an LSM storage engine that survives crashes, and an HTTP server on raw TCP.

The repos are TypeScript with no dependencies, and Node 23.6 or later runs them directly. They total about 3,100 lines across ten projects and 48 tests. Each part covers what the real system does and why, an animation of its core mechanism, a tour of the code with the important lines, how to run it, and exercises that take it toward the real thing. The other courses explain these systems from the outside. This one explains them from the inside.