Not so much a web game as a web game development environment, turtleSpaces uses the simple Logo teaching language to allow users to create 2D and 3D art, animations, models and yes, games!
You can check out this fully-commented listing of a pilotwings-style game here:
https://turtlespaces.org/weblogo/?pub=182
The backend is written in Golang and compiled to WebAssembly, while the frontend is Javascript.