Automatically detect JS errors

src/js/notes.js

@@ -83,6 +83,7 @@ $(function () {
             dataType: 'json'
         });
     }
+
     retagContent();
 });
 
@@ -105,9 +106,11 @@ function retagContent() {
     $("table").wrap("<div class='table-wrapper'></div>");
 
     // Re-render LaTeX equations
+    if (window.MathJax.typeset !== undefined) {
         window.MathJax.texReset();
         window.MathJax.typesetClear();
         window.MathJax.typeset();
+    }
 
     // Re-render Mermaid diagrams
     mermaid.init()

src/python/notes_test.py

@@ -14,6 +14,12 @@ def _launch():
     return browser
 
 
+def assert_no_javascript_errors(browser):
+    assert len(browser.find_elements_by_css_selector(".js-error")) == 0, (
+        "Javascript errors found. See browser console for more details."
+    )
+
+
 def test_index_should_redirect_to_edit():
     browser = _launch()
     browser.get(INDEX_URL)
@@ -24,6 +30,7 @@ def test_index_should_redirect_to_edit():
 def test_should_edit():
     browser = _launch()
     browser.get(INDEX_URL)
+    assert_no_javascript_errors(browser)
 
     # Type a new note
     user_input = browser.find_element_by_id("userInput")
@@ -37,6 +44,7 @@ def test_should_edit():
         "maximus turpis id egestas rhoncus. Morbi eget bibendum leo. "
     )
     sleep(1)
+    assert_no_javascript_errors(browser)
 
     # Should render the preview
     h1 = browser.find_element_by_css_selector("h1")
@@ -48,6 +56,7 @@ def test_should_edit():
 
     # Click view and verify content
     browser.find_element_by_link_text("View").click()
+    assert_no_javascript_errors(browser)
     assert "/view" in browser.current_url
     h1 = browser.find_element_by_css_selector("h1")
     assert h1.text == "Hello world"
@@ -56,6 +65,7 @@ def test_should_edit():
 
     # Click publish and verify content
     browser.find_element_by_link_text("Publish").click()
+    assert_no_javascript_errors(browser)
     h1 = browser.find_element_by_css_selector("h1")
     assert h1.text == "Hello world"
     assert "Hello world" in browser.title

src/templates/index.tmpl

@@ -5,6 +5,13 @@
         <meta name="viewport" content="width=device-width, initial-scale=1">
         <meta name="referrer" content="no-referrer">
 
+        <script type="text/javascript">
+            window.addEventListener('error', function () {
+                html = document.getElementsByTagName("html")[0];
+                html.classList.add("js-error");
+            }, true);
+        </script>
+
         <link rel="stylesheet" href="/static/lib/dropzone.css">
         <link rel="stylesheet" type="text/css" href="/static/lib/github-markdown.css">
         <link rel="stylesheet" type="text/css" href="/static/lib/menus-min.css">