Fix JavaScript null error on home and splash layouts (#4939)

assets/js/_main.js

@@ -123,21 +123,25 @@ $(document).ready(function () {
   });
 
   // Add anchors for headings
-  document
+  (function () {
-    .querySelector(".page__content")
+    var pageContentElement = document.querySelector(".page__content");
-    .querySelectorAll("h1, h2, h3, h4, h5, h6")
+    if (!pageContentElement) return;
-    .forEach(function (element) {
+
-      var id = element.getAttribute("id");
+    pageContentElement
-      if (id) {
+      .querySelectorAll("h1, h2, h3, h4, h5, h6")
-        var anchor = document.createElement("a");
+      .forEach(function (element) {
-        anchor.className = "header-link";
+        var id = element.getAttribute("id");
-        anchor.href = "#" + id;
+        if (id) {
-        anchor.innerHTML =
+          var anchor = document.createElement("a");
-          '<span class="sr-only">Permalink</span><i class="fas fa-link"></i>';
+          anchor.className = "header-link";
-        anchor.title = "Permalink";
+          anchor.href = "#" + id;
-        element.appendChild(anchor);
+          anchor.innerHTML =
-      }
+            '<span class="sr-only">Permalink</span><i class="fas fa-link"></i>';
-    });
+          anchor.title = "Permalink";
+          element.appendChild(anchor);
+        }
+      });
+  })();
 
   // Add copy button for <pre> blocks
   var copyText = function (text) {