LaTeX.js requires a DOM to function--VSCode on Electron does not have a DOM, so rendering is done inside the webview (that contains a DOM). There are ways to get around this (such as jsdom), but it is not that straightforward.
Compilation requires passing the generated HTML from the webview to the extension, I will look into this if there is demand.
There can be an option for selecting the LaTeX.js version wanted, I will add this feature if there exists a need.
