Fallback on missing MathJax

[alexcjohnson]

Discovered while writing tests... it would be nice if text designed for MathJax would still render, as regular text, when MathJax is not found in the global namespace. Currently it just crashes.

[rreusser]

See also (loosely related): plotly/plotly.py#515

[archmoj]

Is this still an issue?

[alexcjohnson]

Dunno, this was filed before we had a habit of including codepens with every bug report. Obviously not a very high priority though 🙃