Basic Comment Preview

Demo: https://vincenttam.gitlab.io/bhdemo

Technologies used:

1. KaTeX math rendering (I added some more popular delimiters to the default ones.)
2. Showdown Markdown parsing

Limitations:

• Hugo and Showdown have different flavor of Markdown by default
• Custom KaTeX macros are not supported unless you inject them into where renderMathInElement is called.