Author here. P5JS is great and I've used it in the past. However you can get pretty far with just VanillaJS. Here's the source code to the ASCII Clouds tool, it's almost all plain JS.
https://github.com/caidanw/caidanw.github.io/blob/main/src/p...
https://github.com/caidanw/caidanw.github.io/blob/main/src/p...
For those curious what a stripped-down version of noise-based clouds would look like, it's only 50 lines of js: https://editor.p5js.org/stungeye/sketches/LPdeHgz9B