From the post:

Yes you heard that right, this game is written entirely in Typescript type annotations, which—if you didn’t know—are Turing complete.

So how the hell am I runnning it in the browser and rendering the game in Typescript types?

The basic rundown is that I created a type-level Typescript runtime, allowing Typescript types to be run outside of the Typescript compiler/language server.

This “runtime” is a custom VM implemented in Zig, which executes a custom bytecode format I compile Typescript code into.