`\def` macro parsing: Trailing spaces in parameter text treated as mandatory delimiters

[hbghlyj]

Description:
LaTeX (or plain TeX) users often add trailing spaces within macro definitions for readability. However, in MathJax, the following definition fails:

$\def\id #1 {#1} \id{1}$

It seems MathJax is treat the space after #1 as a delimiter. Is this strict behavior intended for MathJax's \def implementation?

[dpvc]

Thanks for the report. You are correct, this is an error. It comes from the processing of templated definitions, but if there is no other template, it should drop trailing spaces. I will make a PR to fix it.

For now, you can use the following configuration to work around the problem:

MathJax = {
  loader: {
    '[tex]/newcommand': {
      ready() {
        const {NewcommandUtil} = MathJax._.input.tex.newcommand.NewcommandUtil;
        Object.assign(NewcommandUtil, {
          _GetTemplate_: NewcommandUtil.GetTemplate,
          GetTemplate(parser, cmd, cs) {
            let result = this._GetTemplate_(parser, cmd, cs);
            if (Array.isArray(result) && result.slice(1).join('').replace(/^ +/, '') === '') {
              result = parseInt(result[0]);
            }
            return result;
          }
        });
      }
    }
  }
};

[dpvc]

A slightly better work-around is

MathJax = {
  loader: {
    '[tex]/newcommand': {
      ready() {
        const {NewcommandUtil} = MathJax._.input.tex.newcommand.NewcommandUtil;
        Object.assign(NewcommandUtil, {
          _GetTemplate_: NewcommandUtil.GetTemplate,
          GetTemplate(parser, cmd, cs) {
            let result = this._GetTemplate_(parser, cmd, cs);
            if (Array.isArray(result)) {
              const n = result.length - 1;
              if (result.slice(1, n).join('') === '' && result[n].replace(/^ +/, '') === '') {
                result = parseInt(result[0]);
              }
            }
            return result;
          }
        });
      }
    }
  }
};

as this accounts for templates that have legal spaces, as in \def\id#1 #2{#1,#2} where the space is significant.