Defining custom macros is not possible with Katex

[abdalazizrashid]

Bug description

Enabling katex for doesn't expand macros

Steps to reproduce

---
format:
  html:
    html-math-method: katex
    include-in-header:
       text: |
        $$\newcommand{\E}{\mathbb{E}}$$
---

$\E$

Expected behavior

---
format:
  html:
    # html-math-method: katex
    include-in-header:
       text: |
        $$\newcommand{\E}{\mathbb{E}}$$
---

$\E$

Actual behavior

Your environment

• Quarto 1.4.489
• macOS Sonoma

Quarto check output

Quarto 1.4.489
[✓] Checking versions of quarto binary dependencies...
Pandoc version 3.1.8: OK
Dart Sass version 1.55.0: OK
Deno version 1.33.4: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
Version: 1.4.489
Path: /Applications/quarto/bin

[✓] Checking tools....................OK
TinyTeX: (not installed)
Chromium: (not installed)

[✓] Checking LaTeX....................OK
Using: Installation From Path
Path: /Library/TeX/texbin
Version: 2022

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
Version: 3.11.4
Path: /opt/homebrew/opt/python@3.11/bin/python3.11
Jupyter: 5.5.0
Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........OK
Version: 4.2.0
Path: /Library/Frameworks/R.framework/Resources
LibPaths:
- /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library
knitr: (None)
rmarkdown: (None)

  The rmarkdown package is not available in this R installation.
  Install with install.packages("rmarkdown")

[mcanouil]

Could please edit your title and/or post as currently it is very confusing?
Your title mentioned KaTeX, your post is using HTML.

Also I am pretty sure, using a LaTeX macro definition is not going to work for JavaScript Math libraries such as KaTeX or MathJax.
Please take a look at the library's documentation on how to define custom macros:

• https://katex.org/docs/supported.html#macros
• https://katex.org/docs/options.html

[cscheid]

EDIT: (I was wrong about katex vs mathjax)

@mcanouil It's pretty wild, but it kind of works. This works, for example:

---
format: html
---

$\newcommand{\E}{\mathbb{E}}$

## Hello.

$\E$

What's going on here is that MathJax actually knows how to deal with \newcommand.

But katex doesn't. That's not something we can fix.

[mcanouil]

Pandoc does let those passthrough as for LaTeX format and those libraries catch them in the body. 🤔😮

By the way, that's how it is stated in KaTeX documentation.
if you want to define macro in the header, you need actual JavaScript code (also documented in KaTeX documentation).

if it does not work, it might a matter of version.

[cderv]

Pandoc does let those passthrough as for LaTeX format and those libraries catch them in the body.

You can defined Macros for MathJax in a math block and this will be available to other math block. https://docs.mathjax.org/en/latest/input/tex/macros.html?highlight=defining-tex-macros#defining-tex-macros
So I don't think this is related to Pandoc letting those passthrough. Pandoc sees a Math block and make it a Mathjax compatible block syntax in HTML. Then Mathajx will process the \newcommand inside the math block.

But katex doesn't. That's not something we can fix.

KaTeX will by default do the opposite and consider each Math Block as independent in term of rendering. This means that a \newcommand in a blog will only apply to the current block

---
format: html
---

## Hello.

$$
\newcommand{\E}{\mathbb{E}}
\E
$$

It can work as Mathjax but I believe it requires to set the option globalGroup in katex.render(). Currently Pandoc does not allow to configure that, and Quarto does not modifies this.

There may be a KaTeX way but does not seem as easy as with MathJax through a script in header.

So I am not even sure there is a way to add Macros with KaTeX renderer easily without post processing the HTML.
Maybe this is something we can offer with Quarto 🤔

i'll poke around

[cderv]

Side note from my tries:

• globalGroup: true works when post processing the HTML to add it for test

• Inserting this JS command

   katex.renderToString("\\newcommand{\\E}{\\mathbb{E}", {macros, globalGroup: true})
  

  but
  * It needs to be after var macros is defined
  * Before the other call to katex.render. Not possible right now with pandoc and Quarto

• Doing var macros = {"\\E": "\\mathbb{E}"}; also in postprocessing HTML for test works, but still now way to change this from Pandoc variable, and from Quarto for now.

[cderv]

@cscheid For future reference, I will reopen this as this is something we may want to consider adding until Pandoc supports it maybe - we already post process HTML for KaTeX related tweaks so we could probably offer the feature at some point if this is useful to users.