firefox debugger

.vscode/launch.json

@@ -0,0 +1,16 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch localhost",
+            "type": "firefox",
+            "request": "launch",
+            "reAttach": true,
+            "url": "http://localhost:3000/index.html",
+            "webRoot": "${workspaceFolder}/book"
+        },
+    ]
+}

scripts/sidebar.js

@@ -22,6 +22,9 @@ var updateFunction = function() {
         el.classList.remove("active");
     });
 
+    if (id == undefined)
+        return;
+
     Array.prototype.forEach.call(document.getElementsByClassName("pagetoc")[0].children, function(el) {
         if (id.href.localeCompare(el.href) == 0) {
             el.classList.add("active");