Answer 1

You can't use OpenGL directly in web browser-based JavaScript.

You can use WebGL which uses OpenGL, though.

Here is a tutorial on WebGL:
https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/Tutorial

I have several codes in my profile that use WebGL.

I used WebGL through a JavaScript library called three.js here:
https://code.sololearn.com/WqG6xi6CqDrm/#html

I used WebGL to make a volumetric ray tracing renderer for a julia set fractal here:
https://code.sololearn.com/W6e6xWN0T7Jv/#html