Add support for KaTeX HTML math

Closes #1626

2 files changed, 20 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Options.hs b/src/Text/Pandoc/Options.hs
index 84ccbbdc9..ebfd8f8a9 100644
--- a/src/Text/Pandoc/Options.hs
+++ b/src/Text/Pandoc/Options.hs
@@ -251,6 +251,7 @@ data HTMLMathMethod = PlainMath
                     | WebTeX String               -- url of TeX->image script.
                     | MathML (Maybe String)       -- url of MathMLinHTML.js
                     | MathJax String              -- url of MathJax.js
+                    | KaTeX String String -- url of stylesheet and katex.js
                     deriving (Show, Read, Eq)
 
 data CiteMethod = Citeproc                        -- use citeproc to render them
diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index 8106806cf..652fc979f 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -157,6 +157,10 @@ pandocToHtml opts (Pandoc meta blocks) = do
                               H.script ! A.src (toValue url)
                                        ! A.type_ "text/javascript"
                                        $ mempty
+                           KaTeX js css ->
+                              (H.script ! A.src (toValue js) $ mempty) <>
+                              (H.link ! A.rel "stylesheet" ! A.href (toValue css)) <>
+                              (H.script ! A.type_ "text/javascript" $ toHtml renderKaTeX)
                            _ -> case lookup "mathml-script" (writerVariables opts) of
                                       Just s | not (writerHtml5 opts) ->
                                         H.script ! A.type_ "text/javascript"
@@ -728,6 +732,10 @@ inlineToHtml opts inline =
                                   case t of
                                     InlineMath  -> "\\(" ++ str ++ "\\)"
                                     DisplayMath -> "\\[" ++ str ++ "\\]"
+                               KaTeX _ _ -> return $ H.span ! A.class_ "math" $
+                                  toHtml (case t of
+                                            InlineMath -> str
+                                            DisplayMath -> "\\displaystyle " ++ str)
                                PlainMath -> do
                                   x <- inlineListToHtml opts (texMathToInlines t str)
                                   let m = H.span ! A.class_ "math" $ x
@@ -829,3 +837,14 @@ blockListToNote opts ref blocks =
                               Just EPUB3 -> noteItem ! customAttribute "epub:type" "footnote"
                               _          -> noteItem
          return $ nl opts >> noteItem'
+
+-- Javascript snippet to render all KaTeX elements
+renderKaTeX :: String
+renderKaTeX = unlines [
+    "window.onload = function(){var mathElements = document.getElementsByClassName(\"math\");"
+  , "for (var i=0; i < mathElements.length; i++)"
+  , "{"
+  , " var texText = mathElements[i].firstChild"
+  , " katex.render(texText.data, mathElements[i])"
+  , "}}"
+  ]