How to LaTeX in Jekyll using KaTeX
11 January 2021
[ website , latex ]

The kramdown parser, default for many jekyll blogs, generates math code using MathJax, a much slower alternative to KaTeX. There are many ways people have sought to get around this to transform math/tex scripts into \(\KaTeX\) on the client side: Like this or this. I found this to be cumbersome.

The easiest way I found was to use the \(\KaTeX\) auto-render extension, if you use GitHub pages for your website. Alternatively you can render server side if you directly set up kramdown-math-katex by following this very informative blog.


Step 1: Adding KaTeX

Turn on the KaTeX engine by adding this to your _config.yaml:

kramdown:
  math_engine: katex

Step 2: Render \(\KaTeX\)

Method 1: Using the auto-render extension (works for GitHub pages)

We use the auto-renderer option. In your _includes/head.html, add:

<head>

  ...

  <!--KaTeX-->
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.12.0/dist/katex.min.css" integrity="sha384-AfEj0r4/OFrOo5t7NnNe46zW/tFgW6x/bCJG8FqQCEo3+Aro6EYUG4+cU+KJWu/X" crossorigin="anonymous">
  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.12.0/dist/katex.min.js" integrity="sha384-g7c+Jr9ZivxKLnZTDUhnkOnsh30B4H0rpLUpJ4jAIKs4fnJI+sEnkvrMWph2EDg4" crossorigin="anonymous"></script>
  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.12.0/dist/contrib/auto-render.min.js" integrity="sha384-mll67QQFJfxn0IYznZYonOWZ644AWYC+Pt2cHqMaRhXVrursRwvLnLaebdGIlYNa" crossorigin="anonymous"></script>
  <script>
      document.addEventListener("DOMContentLoaded", function() {
          renderMathInElement(document.body, {
              // ...options...
          });
      });
  </script>

</head>

Method 2: Using kramdown-math-katex

Convert formulas to HTML

Then, on your computer, install the kramdown-math-katex package in Ruby:

gem install kramdown-math-katex

kramdown-math-katex requires a few dependencies, install them like so:

gem install katex
gem install execjs

and one of the following javascript engines, if you dont already have them installed:

gem install therubyracer
gem install therubyrhino
gem install duktape

Render HTML into \(\LaTeX\) fonts

Given that we’ve converted everything into HTML, we now need to render the fonts in the browser using some CSS and various fonts. To do that, we can follow the \(\KaTeX\) starter template.

As noted by Guillaume we do not need to add the javascripts since we’ve already obtained the HTML. Therefore, in your _includes/head.html, you just need to add:

<head>

  ...

  <!-- KaTeX -->
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.12.0/dist/katex.min.css" integrity="sha384-AfEj0r4/OFrOo5t7NnNe46zW/tFgW6x/bCJG8FqQCEo3+Aro6EYUG4+cU+KJWu/X" crossorigin="anonymous">

</head>

He also suggests downloading the relevant CSS files and font files only for rendering without an internet connection. Therefore, you can also download the latest version of \(\KaTeX\) and then only keeping the katex.min.css file and the fonts/ folder. That way, your snippet will be like:

<head>

  ...

  <!-- KaTeX -->
  <link rel="stylesheet" href="/assets/plugins/katex.0.11.1/katex.min.css">

</head>

Step 3: Toggle on and off (optional)

Lastly, we can make this even more lightweight by adding a toggle on and off option to make other pages more lightweight. To do so, we modify the above script by adding a page property called katex and surround the relevant lines with a conditional:

<head>

  ...

  
  <!-- KaTeX -->
  <link rel="stylesheet" href="/assets/plugins/katex.0.11.1/katex.min.css">
  

</head>

Step 4: To use

To every blog page that you intend to use katex, add katex: True to your preamble, like so:

---
layout: post
title: KaTeX with Jekyll
katex: True
---
inline: $$f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi$$
display mode (centered):

$$f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi$$

And this gives:

inline: \(f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi\)

display mode (centered):

\[f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi\]

Now if you toggle the katex property, you can see that the HTML symbols are created, but they will not load in \(\LaTeX\) font.

Fast \(\LaTeX\) to \(\KaTeX\) commands

There’s a quick list and a complete list of supported functions.

Some of the canonical ones:

  • Inline: $x$ to $$x$$ with no line spacing before or after (see above).
  • Standalone: $$f=ma$$ to $$f=ma$$ with line spacing before and after (see above).
  • Equation labeling: \label{eq:test} to \tag{1} (manually labeled equations)
  • Haven’t figured out how to do bibtex

Notes

I first transcribe a \(\LaTeX\) document into github-flavored markdown (GFM) using pandoc:

pandoc -f latex -t markdown file.tex

This is really nice because it actually converts all of my custom macros into just plain latex, which is good enough most of the time. However, the above modifications (inline, standalone, any labeling) will need to be made after the transcription in order for it to work with \(\KaTeX\).

Things to edit after transcribing:

  • Pandoc doesn’t transcribe two of ^ in sequence well, but you can fix that manually.
  • Pandoc adds an extra \ at the end of a paragraph. This needs to be removed.
  • Can remove the \nonumber attribute in equations.
  • Equation referencing isn’t available, therefore add appropriate \tag{} attributes and label them manually.