This is a simple implementation of LaTeX xparse package for MathJax. Currently it provides three family of commands:

• NewDocumentCommand (also Renew..., Provide... and Declare... variants as aliases);
• IfBooleanTF (also T and F variants);
• IfNoValueTF (also T and F variants).

Supported argument type specifiers are:

• m: mandatory argument;
• o: optional argument;
• O⟨default⟩: optional argument with default;
• s: optional star;
• t⟨token⟩: optional token.

Please refer to xparse documentation on CTAN for more information about the commands.

Note that NewDocumentEnviroment is not implemented but should not be hard to do so. There are also many other argument types that could be implemented with varying degrees of difficulty.

There is a packed minified version under browser. You can serve it under your website (say, at /path/to/xparsejax.js) and load it in your MathJax configuration like so:

MathJax = {
  loader: {
    load: ['[xparsejax]/xparsejax.js'],
    paths: {xparsejax: '/path/to'} // specify your path here
  },
  tex: {
    packages: {'[ ]': ['xparsejax']},
  },
  [... other stuff ...]
}

To compile it yourself, you should have both node and pnpm installed. Then it should suffice to do:

cd xparsejax
npm install
npm run build