Mathjax works!

R/bulma_document.R

 #' ---
 #' ```
 #'
+#' @inheritParams rmarkdown::html_document_base
 #' @inheritDotParams rmarkdown::html_document_base
 #' @export
 bulma_document <- function(
   dev = "png",
   toc = FALSE,
   toc_depth = 3,
+  mathjax = "default",
   pandoc_args = NULL,
   extra_dependencies = NULL
 ) {
 
   pandoc_args <- c(pandoc_args, rmarkdown::pandoc_toc_args(toc, toc_depth))
 
+  mathjax_url <- if (mathjax %in% c("default", "local")) {
+    mathjax_local <- Sys.getenv("RMARKDOWN_MATHJAX_PATH", unset = NA)
+    if (mathjax == "local" && is.na(mathjax_local)) {
+        rlang::warn(
+          glue("Please use `Sys.setenv('RMARKDOWN_MATHJAX_PATH')` to set local mathjax location.",
+               "Falling back to online mathjax from https://mathjax.rstudio.com")
+        )
+      }
+    mathjax_path <- ifelse(mathjax == "default" || is.na(mathjax_local),
+                           "https://mathjax.rstudio.com/latest",
+                           mathjax_local)
+    file.path(mathjax_path, "MathJax.js?config=TeX-AMS-MML_HTMLorMML")
+  } else mathjax
+
+  if (!is.null(mathjax_url)) {
+    pandoc_args <- c(pandoc_args, "--mathjax", "--variable",
+                     paste0("mathjax-url:", mathjax_url))
+  }
+
   rmarkdown::output_format(
     knitr = rmarkdown::knitr_options_html(
       fig_width, fig_height, fig_retina, keep_md, dev
     base_format = rmarkdown::html_document_base(
       self_contained = TRUE, template = NULL,
       pandoc_args = pandoc_args,
+      mathjax = mathjax,
       extra_dependencies = extra_dependencies
     )
   )

inst/bulma/bulma.html

 $if(mathjax-url)$
 <!-- dynamically load mathjax for compatibility with self-contained -->
 <script>
-  (function () {
-    var script = document.createElement("script");
-    script.type = "text/javascript";
-    script.src  = "$mathjax-url$";
-    document.getElementsByTagName("head")[0].appendChild(script);
-  })();
+document.addEventListener("DOMContentLoaded", function(event) {
+  var script = document.createElement("script");
+  script.type = "text/javascript";
+  script.src  = "$mathjax-url$";
+  document.getElementsByTagName("head")[0].appendChild(script);
+});
 </script>
 $endif$
 

man/bulma_document.Rd

 \usage{
 bulma_document(..., css = NULL, fig_width = 10, fig_height = 7,
   fig_retina = 2, keep_md = FALSE, dev = "png", toc = FALSE,
-  toc_depth = 3, pandoc_args = NULL, extra_dependencies = NULL)
+  toc_depth = 3, mathjax = "default", pandoc_args = NULL,
+  extra_dependencies = NULL)
 }
 \arguments{
+\item{...}{Ignored}
+
+\item{mathjax}{Include mathjax. The "default" option uses an https URL from a
+MathJax CDN. The "local" option uses a local version of MathJax (which is
+copied into the output directory). You can pass an alternate URL or pass
+\code{NULL} to exclude MathJax entirely.}
+
+\item{pandoc_args}{Additional command line options to pass to pandoc}
+
+\item{extra_dependencies}{Extra dependencies}
+
 \item{...}{Arguments passed on to \code{rmarkdown::html_document_base}
 \describe{
   \item{smart}{Produce typographically correct output, converting straight