mhchem TeX extension breaks internally when leaving out closing bracket

[wb-joona]

Issue Summary

TeX mhchem input extension produces an error from the internals when not closing the \ce command.

Steps to Reproduce:

Live minimal reproducible example here: https://codesandbox.io/s/nice-dhawan-yu49p?file=/index.html

1. Load latest tex-chtml.js
2. Render the equation \ce{H2O
3. Notice uncaught error:

TypeError: t.slice is not a function
    at u.Machine (mhchem.js:1:410)
    at e.parse (tex-chtml.js:1:245691)
    at t.parse (tex-chtml.js:1:212776)
    at t.parse (tex-chtml.js:1:256801)
    at t.controlSequence (tex-chtml.js:1:220763)
    at e.t.parse (tex-chtml.js:1:243417)
    at t.parse (tex-chtml.js:1:212776)
    at t.parse (tex-chtml.js:1:256801)
    at t.Parse (tex-chtml.js:1:257409)
    at new t (tex-chtml.js:1:256142)
    at e.compile (tex-chtml.js:1:197284)
    at e.t.compile (tex-chtml.js:1:44978)
    at Object.renderMath (tex-chtml.js:1:35007)
    at e.renderConvert (tex-chtml.js:1:35820)
    at e.t.convert (tex-chtml.js:1:44865)
    at e.t.convert (tex-chtml.js:1:38921)
    at tex-chtml.js:1:22644
    at e (tex-chtml.js:1:717213)
    at new Promise (<anonymous>)
    at Object.e.handleRetriesFor (tex-chtml.js:1:717178)
    at Object.e.MathJax.<computed> [as tex2chtmlPromise] (tex-chtml.js:1:22597)
    at convert (yu49p.csb.app/:57:17)
    at HTMLInputElement.onclick (yu49p.csb.app/:133:11)

I would expect that with noerrors loaded, I would see some output at least. This error appears to break the rendering though.

The error appears to be originating here:
https://github.com/mathjax/MathJax-src/blob/2dd53ce6c8af3c9cceba0baf014ea9b065130774/ts/input/tex/mhchem/MhchemConfiguration.ts#L51-L53

The catch appears to assume that the error is an array, but the actual error emitted here is the following object:

{
  id: 'MissingCloseBrace',
  message: 'Missing close brace'
}

and thus there is no .slice().

Technical details:

• MathJax Version: 3.2.0
• Client OS: Windows 10 Pro
• Browser: Chrome 98.0.4758.82

Supporting information:

• Please supply a link to a (live) minimal example page, when possible.
  • https://codesandbox.io/s/nice-dhawan-yu49p?file=/index.html
• If your issue is with the display of the mathematics produced by MathJax, include a screen snapshot that illustrates the problem, when possible.
• Check your browser console window for any error messages, and include them here.
• Include the MathJax configuration you are using, and the script tag that loads MathJax itself.

<script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
<script>
    window.MathJax = {
        loader: { load: ["[tex]/noerrors", "[tex]/mhchem"] },
        tex: { packages: { "[+]": ["noerrors", "mhchem"] } },
    };
</script>
<script
    id="MathJax-script"
    async
    src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js"
></script>

[pkra]

https://github.com/mhchem/MathJax-mhchem/ is a better place for mhchem issues. mhchem/MathJax-mhchem#20 looks potentially similar.

[wb-joona]

Thanks! Looks like a match indeed.

[wb-joona]

On another thought, I'm not sure if the issue is with mhchem, but with the integration of the extension in the MathJax code. The issue is that the MhchemConfiguration file's catch assumes that the error is an array instead of an object, which is on MathJax' side - not mhchem's side.

[mhchem]

@wb-joona, thanks a lot for this bugreport, in particular your live minimal reproducible example. That was very helpful.

The issue is in MhchemConfiguration.ts

  try {
    let arg = parser.GetArgument(name);
    let tex = mhchemParser.toTex(arg, machine);
    parser.string = tex + parser.string.substr(parser.i);
    parser.i = 0;
  } catch (err) {
    throw new TexError(err[0], err[1], err.slice(2));
  }

Link to Source

The issue is that the first line (parser.GetArgument()) throws errors as TexError ({id: ..., message: ...}), while the mhchemParser in the 2nd line throws errors as an array of two strings (['id', 'message']).

As the TeXErrors are catched further above, anyway, it should be enough to "try" mhchemParser, shouldn't it? @pkra, @zorkow

  let arg = parser.GetArgument(name);
  try {
    let tex = mhchemParser.toTex(arg, machine);
  } catch (err) {
    throw new TexError(err[0], err[1]);
  }
  parser.string = tex + parser.string.substr(parser.i);
  parser.i = 0;

[dpvc]

I have made a PR to address the issue based on @mhchem 's suggestion, which was right on target.