From d3402bcd308cf9b115628c13e9e20ad532f43fe8 Mon Sep 17 00:00:00 2001
From: Martin von Gagern <gagern@ma.tum.de>
Date: Sun, 15 Jan 2017 17:47:02 +0100
Subject: [PATCH] Show katex errors in HTML output if rendering fails

---
 main.css |  4 ++++
 main.js  | 13 ++++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/main.css b/main.css
index 17a95fcc5..a33d29e57 100644
--- a/main.css
+++ b/main.css
@@ -206,3 +206,7 @@ body {
 .credits a {
     color: white;
 }
+
+.errorMessage {
+    color: red;
+}
\ No newline at end of file
diff --git a/main.js b/main.js
index ad9e8a5de..cad88cd23 100644
--- a/main.js
+++ b/main.js
@@ -8,7 +8,18 @@ window.startup = function() {
     var demoOutput = document.getElementById("demo-output");
 
     function doDemo() {
-        katex.render("\\displaystyle{" + demoInput.value + "}", demoOutput);
+        try {
+            katex.render("\\displaystyle{" + demoInput.value + "}", demoOutput);
+        } catch(err) {
+            while(demoOutput.lastChild) {
+                demoOutput.removeChild(demoOutput.lastChild);
+            }
+            var msg = document.createTextNode(err.message);
+            var span = document.createElement("span");
+            span.appendChild(msg);
+            demoOutput.appendChild(span);
+            span.setAttribute("class", "errorMessage");
+        }
     }
 
     demoInput.addEventListener("input", function() {