Custom MathJax URL not working

[timwaite]

Thanks for the great package!

Custom URLs for MathJax aren't working for me in Bookdown. I have tried setting the mathjax option in _output.yml as below. However the rendered HTML just uses the out of date version 2.7.2 of MathJax from mathjax.rstudio.com/latest, not the version I have specified.

Am I doing something wrong, or is this a bug?

I can see in RStudio that the mathjax variable argument has been passed to the pandoc command line call. However it seems that the variable isn't being processed into the template gitbook.html.

I asked asked about this on StackOverflow, but I got no response. [Edit: fixed link]

Minimal example:

_output.yml:

bookdown::gitbook:
  css: style.css
  mathjax: "https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js" 

index.Rmd:

--- 
title: "Untitled"
author: "An author"
site: bookdown::bookdown_site
documentclass: book
---

$$E=mc^2$$

Session info:

> xfun::session_info('rmarkdown')
R version 3.6.3 (2020-02-29)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Mojave 10.14.6, RStudio 1.3.959

Locale: en_GB.UTF-8 / en_GB.UTF-8 / en_GB.UTF-8 / C / en_GB.UTF-8 / en_GB.UTF-8

Package version:
  base64enc_0.1.3 digest_0.6.25   evaluate_0.14  
  glue_1.4.1      graphics_3.6.3  grDevices_3.6.3
  highr_0.8       htmltools_0.5.0 jsonlite_1.7.0 
  knitr_1.29      magrittr_1.5    markdown_1.1   
  methods_3.6.3   mime_0.9        rlang_0.4.7    
  rmarkdown_2.3   stats_3.6.3     stringi_1.4.6  
  stringr_1.4.0   tinytex_0.24    tools_3.6.3    
  utils_3.6.3     xfun_0.15       yaml_2.2.1     

Pandoc version: 2.9.2.1

---

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[cderv]

Yes I think this is a bug.

In bookdown, to change the mathjax CDN used by gitbook, currently I think this should be passed as pandoc variable in index.Rmd yaml header because the template use a special js script

bookdown/inst/templates/gitbook.html

Lines 169 to 183 in aa6bd19

	$if(math)$
	<!-- dynamically load mathjax for compatibility with self-contained -->
	<script>
	(function () {
	var script = document.createElement("script");
	script.type = "text/javascript";
	var src = "$if(mathjax)$$mathjax$$endif$";
	if (src === "" || src === "true") src = "https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-MML-AM_CHTML";
	if (location.protocol !== "file:")
	if (/^https?:/.test(src))
	src = src.replace(/^https?:/, '');
	script.src = src;
	document.getElementsByTagName("head")[0].appendChild(script);
	})();
	</script>

however, this does not behave as it should either, because

mathjax: "https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"

is rendered as a html link before being passed to pandoc template. I need to understand why.

Anyway, I think it should work as you tried.
When passing mathjax in the output format argument, it passes to --mathjax flag in pandoc commandline and this set mathjax variable to true , and mathjaxurl to the url.

I think, that gitbook.html template should use that mathjaxurl variable.

Thanks for the report. I'll think about the correct fix

[cderv]

@yihui so I have looked into this and I think we don't currently support properly setting a custom mathjax url with bookdown::gitbook.

Currently, all the mathjax handling is dealt in rmarkdown:::pandoc_mathjax_args mainly. What causing issue here is that rmarkdown does a correct handling only for its internal template (html_document(template = "default")) and as bookdown use its own template, we don't benefit from it in bookdown.

Here my analysis of the situation, to be a base of comparaison with a potential fix; I spend some time on it, mainly to be up to date with how mathjax is handle in rmarkdown and bookdown.

Current situation

# setting some helpers
temp_file <- tempfile(fileext = ".Rmd")
xfun::write_utf8(c(
  "---",
  "title: Test",
  "---",
  "",
  "# test",
  "",
  "$1+1$"
), temp_file)

# this will print the html part of custom mathjax code from RStudio's template
render_gitbook <- function(...) {
  # we insure pandoc 2.7.3 for now
  rmarkdown::find_pandoc(version = "2.7.3")
  res <- xfun::in_dir(tempdir(),
               rmarkdown::render(
                 temp_file, "bookdown::gitbook",
                 output_options = list(...),
                 quiet = TRUE)
  )
  html <- xfun::read_utf8(res)
  i <- grep("<!-- dynamically load mathjax for compatibility with self-contained -->",
       html)
  if (!length(i)) return("no Mathjax")
  start_s <- grep("<script>", html)
  end_s <- grep("</script>", html)
  xfun::raw_string(html[start_s[start_s > i][1]:end_s[end_s>i][1]])
}

custom_mathjax <- "https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"

Let's note first that bookdown::gitbook with self_contained = TRUE does not work because mathjax won't be included. I think it should as we ofter to customise self_contained argument.
In fact this is due to the handling of mathjax in rmarkdown:::pandoc_mathjax_arg which remove mathjax is another template than the one included with rmarkdown. Obviously, bookdown::gitbook() is using another template

render_gitbook(self_contained = TRUE)
#> Warning: MathJax doesn't work with self_contained when not using the rmarkdown
#> "default" template.
#> [1] "no Mathjax"
render_gitbook(self_contained = TRUE, mathjax = custom_mathjax)
#> Warning: MathJax doesn't work with self_contained when not using the rmarkdown
#> "default" template.
#> [1] "no Mathjax"

Now on our issue here, currently custom url is not taken into account in the gitbook template. This is because only mathjax pandoc variable is used (and it is logical with no value set)

render_gitbook(mathjax = custom_mathjax)
#> <script>
#>   (function () {
#>     var script = document.createElement("script");
#>     script.type = "text/javascript";
#>     var src = "true";
#>     if (src === "" || src === "true") src = "https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-MML-AM_CHTML";
#>     if (location.protocol !== "file:")
#>       if (/^https?:/.test(src))
#>         src = src.replace(/^https?:/, '');
#>     script.src = src;
#>     document.getElementsByTagName("head")[0].appendChild(script);
#>   })();
#> </script>

Then, mathjax = "local" is not supported in gitbook either - the included code is still the same.

render_gitbook(mathjax = "local")
#> <script>
#>   (function () {
#>     var script = document.createElement("script");
#>     script.type = "text/javascript";
#>     var src = "true";
#>     if (src === "" || src === "true") src = "https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-MML-AM_CHTML";
#>     if (location.protocol !== "file:")
#>       if (/^https?:/.test(src))
#>         src = src.replace(/^https?:/, '');
#>     script.src = src;
#>     document.getElementsByTagName("head")[0].appendChild(script);
#>   })();
#> </script>

For no mathjax asked, it is working - no mathjax is used.

render_gitbook(mathjax = NULL)
#> [1] "no Mathjax"

I also tried with custom template, it has mostly the same behavior than rmarkdown for now.
We create a dummy template to show the pandoc variables set for the rendering, and we test several scenarios.

# dummy html file
library(htmltools)
html_content <- div(
  # hack to work with previous function render_gitbook
  HTML("<!-- dynamically load mathjax for compatibility with self-contained -->"),
  tags$script(
    p("this is mathjax variable: $mathjax$"),
    br(),
    p("this is mathjaxurl variable: $mathjaxurl$"),
    br(),
    p("this is mathjax-url variable: $mathjax-url$"),
    br(),
    p("this is math variable: $math$")
  )
)
template <- tempfile(fileext = ".html")
xfun::write_utf8(as.character(html_content), template)

# custom templates can use pandoc mathjaxurl variable or math variable
render_gitbook(mathjax = custom_mathjax, template = template)
#>   <script>
#>     <p>this is mathjax variable: true</p>
#>     <br/>
#>     <p>this is mathjaxurl variable: https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js</p>
#>     <br/>
#>     <p>this is mathjax-url variable: </p>
#>     <br/>
#>     <p>this is math variable: <script src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js" type="text/javascript"></script></p>

# same for mathjax = local
render_gitbook(mathjax = "local", template = template)
#>   <script>
#>     <p>this is mathjax variable: true</p>
#>     <br/>
#>     <p>this is mathjaxurl variable: libs/mathjax-local/MathJax.js</p>
#>     <br/>
#>     <p>this is mathjax-url variable: </p>
#>     <br/>
#>     <p>this is math variable: <script src="libs/mathjax-local/MathJax.js?config=TeX-AMS-MML_HTMLorMML" type="text/javascript"></script></p>

# still does work with self_contained = TRUE
render_gitbook(mathjax = custom_mathjax, template = template, self_contained= TRUE)
#> Warning: MathJax doesn't work with self_contained when not using the rmarkdown
#> "default" template.
#>   <script>
#>     <p>this is mathjax variable: </p>
#>     <br/>
#>     <p>this is mathjaxurl variable: </p>
#>     <br/>
#>     <p>this is mathjax-url variable: </p>
#>     <br/>
#>     <p>this is math variable: </p>
#>   </script>

# with default, the pandoc mathjax default and custom template one is used
render_gitbook(template = template)
#>   <script>
#>     <p>this is mathjax variable: true</p>
#>     <br/>
#>     <p>this is mathjaxurl variable: https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.2/MathJax.js</p>
#>     <br/>
#>     <p>this is mathjax-url variable: </p>
#>     <br/>
#>     <p>this is math variable: <script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.2/MathJax.js?config=TeX-AMS_CHTML-full" type="text/javascript"></script></p>

That means that with a custom template, it is to the user responsability to do something based on pandoc feature mainly. (But let's note there is no easy way to get the full url with the query part in mathjaxurl variable)
Rmarkdown mathjax-url is never sets to helps create another self-contained format.

What do we want to do ?

• Do we want to support custom mathjax in gibook() ?
  • If no, nothing to do and we can document then close.
  • If yes, I have some adjustment to make. but first...
• Do we want to support mathjax = "local" also, and more generally have the same behavior in gitbook template than in default.html in rmarkdown ?

Depending on the choices, we could

1. Try to come with a fix in gitbook only ? I have something to PR on this one.
2. Rethink the way it works in rmarkdown so that it is better extensible with other format.

Choice 1 doesn't allow to remove the warning when self_contained = TRUE but choice 2 can enable that. Do we want to support self contained for gitbook (not sure).

I will share the work I have done for 1, but I would be interested in your thinking on all this. Thanks !

[yihui]

Thanks @cderv! I need more time to digest this, but let me ask a quick question first: will it help if we remove the restriction here https://github.com/rstudio/rmarkdown/blob/204aa41faea12212dc80642f5a8e53e4e52e0999/R/pandoc.R#L478-L483?

[cderv]

Yes this is the part in Rmarkdown that is currently activated when using Gitbook. I see two impacts of this :

1. this restriction on self_contained with the warning is to me the cause of bookdown::gitbook() not having mathjax when self_contained = TRUE. In this case, --mathjax is not added to command line pandoc and I guess default pandoc rendering is used. (again I don't know if anyone use some "self contained gitbook" and if it really makes sense - never used it myself). So math appears in the doc (I tried on bookdown-demo) but they are not rendered using mathjax.

2. currently if the default rmarkdown template is not used (by default, we mean template = "default" for html_document only, so the default.html file in rmarkdown), rmarkdown only sets the --mathjax pandoc command line argument.

   args <- c(args, paste(c("--mathjax", mathjax), collapse = "="))

   That is what happens with gitbook() because a custom template is used (from rmarkdown point of view).
   It means we rely on pandoc mathjax handling for template, :

   • $math$ variable that contains the <script> line, transformed when --self-contained is used
   • $mathjax$ variable, logical and equal TRUE is --mathjax is used
   • $mathjaxurl$ variable, contains the url (up until the query part, so before any ?), mainly to be used in default beamer template from my understanding.

   but currently we only support the default Rstudio's mathjax url if mathjax is to be used.
   

   bookdown/inst/templates/gitbook.html

   Lines 175 to 176 in aa6bd19

   	var src = "$if(mathjax)$$mathjax$$endif$";
   	if (src === "" || src === "true") src = "https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-MML-AM_CHTML";

My current PR tries to solve 2 from bookdown directly. If we remove (or change the restriction) on rmarkdown side that would be different. I mentioned that in the PR discussion. 1 is blocked by rmarkdown restriction I guess - we could bypass it but we'll still get the warning.

I am wondering is this rmarkdown restriction is also impacting other 📦 BTW 🤔 - will look into it.

[cderv]

(again I don't know if anyone use some "self contained gitbook" and if it really makes sense - never used it myself).

Another thought on that: If fact, it seems it is really discourage, from an old comment of yours #61 (comment) where you say

Also note MathJax may not work when self_contained = TRUE.

However, it is not really specified in the bookdown book : https://bookdown.org/yihui/bookdown/html.html#gitbook-style
only:

Please note that if you change self_contained = TRUE to make self-contained HTML pages, the total size of all HTML files can be significantly increased since there are many JS and CSS files that have to be embedded in every single HTML file.

I really wonder if we can't force self_contained = FALSE in gitbook and use the $math$ pandoc variable directly in the gitbook.html pandoc template.

[sentausa]

Hi, is there any progress on this? I tried to render a gitbook bookdown with self_contained = TRUE and I got a [WARNING] Could not convert TeX math '\frac{1}{\sum_{i=1}^{S} p_{i}^2}', rendering as TeX or something similar and the equations were not rendered correctly. When I use the equation or equation* environment, it is not even shown. I wonder if it means that bookdown cannot render LaTeX mathematical expressions when using self_contained = TRUE?

[cderv]

hi @sentausa,

did you try this with a custom mathjax url ? If so, this issue is still not solved.

If not, then...

When I use the equation or equation* environment, it is not even shown. I wonder if it means that bookdown cannot render LaTeX mathematical expressions when using self_contained = TRUE?

With default mathjax it works ok.

---
title: test equation
output:
  bookdown::html_document2: 
    self_contained: true
---

First equation

$$
\frac{1}{\sum_{i=1}^{S} p_{i}^2}
$$

Second equation 

\begin{equation*}
\frac{1}{\sum_{i=1}^{S} p_{i}^2}
\end{equation*}

[sentausa]

Bonjour Christophe, thank you for your reply. No, I didn't use a custom mathjax url, and I was trying to render a bookdown::github document. So yeah, perhaps I should change my question: can bookdown::github render LaTeX mathematical expressions when using self_contained = TRUE?

What is html_document2? If it is visually similar to the github bookdown (multiple page, etc.), I might use it instead. Merci!

[cderv]

Thanks for the precision @sentausa

No, I didn't use a custom mathjax url, and I was trying to render a bookdown::github document.

Unfortunately your question is completely out of context with this issue then.
In general, please try to participate in an already open thread when your remarks / questions is in scope with the current issue.

Anyway, this is not harmful - I'll just hide some comments afterwards as off topic.

Several things to anwser:

• github_document is not a format from bookdown but from rmarkdoww. You are in the bookdown repo here. so bookdown::github document does not exist, rmarkdown::github document does
• rmarkdown::github_document is a format to render markdown file using GIthub Flavored Markdown, mainly to be included in Github and previewed by Github. self_contained does not make sense for this format, and so is not an argument of the format. see ?rmarkdown::github_document()
• Also math expresion can't be rendered in github document because Github does not support this in Github Flavor Markdown. So can you can't add maths in markdown to be processed with mathjax.

What is html_document2? If it is visually similar to the github bookdown (multiple page, etc.), I might use it instead. Merci!

This is a bookdown output format. See the documentation: https://bookdown.org/yihui/bookdown

Please ask your question on https://community.rstudio.com next time. It will be easier to point you in the right direction. We are trying to keep Github issue scoped to one topic. Thank you.

[cderv]

Last thing @sentausa , I am under the impression you are in fact talking about bookdown::gitbook not github.

If so, sorry for my previous answer where I misunderstood you. If you have a specific issue with this format, please open a new issue following the issue guide. It will be better than having this discussion in another thread. Thank you very much !

[sentausa]

@cderv, yes indeed it's bookdown::gitbook. Sorry for the confusion (I don't know what happened to my fingers, or my mind)! I'll open a new issue.