You can see this WebGL demo in action right now right here: https://www.anttivainio.net/webgldemo
This is a rather simple 3D WebGL demo. The scene in the demo features a somewhat complex rotating object and a simple fullscreen post processing effect that is achieved using a framebuffer and a shader. In addition the resolution is automatically scaled with the size of the canvas and it is possible to fly around in the scene using WSAD and arrow keys.
The code includes a nice amount of vector and matrix functions for JavaScript and also classes to handle shaders and framebuffers.