These docs are an attempt to help explain some of the helper function used in the articles on webglfundamentals.org.
WebGL is a very low-level API and so using it is very verbose. To draw a simple lighted cube can easily require 50-100 WebGL calls. Calls to create buffers and put data in them. Calls to create that data in the first place. Calls to create GLSL shader programs. Calls read attribute and uniform locations. Calls to create textures, bind textures to texture units, bind buffers to attributes, and set uniforms.
At some point this complexity makes it hard to concentrate on the topic at hand and so helper functions can reduce the number of lines need to a smaller few.
Functions for reducting the amount of code can be found here.
If you're using WebGL to do 2D or 3D you'll likely need many math helper functions in JavaScript as well.
Functions for 2D math are here.
Functions for 3D math are here.
Finally WebGL requires vertices to operate on. Functions to generate veritces for common shapes like spheres, cubes, planes, cones, etc can be found here.
#JSDoc3 Plea
These docs are generated with JSDoc3. I find them very confusing to look at and in some places frustratingly verbose. If you have any experience with JSDoc3 and know how to make the docs more approachable and useful please submit a pull request or file an issue with details.