check if toc exists on floating button click function

Author: fanixus96

scaladoc/resources/dotty_res/scripts/ux.js

@@ -139,14 +139,17 @@ window.addEventListener("DOMContentLoaded", () => {
     }
   })
 
-  // show/hide side menu on mobile view
-  const sideMenuToggler = document.getElementById("mobile-sidebar-toggle");
-  sideMenuToggler.addEventListener('click', _e => {
-    document.getElementById("leftColumn").classList.toggle("show")
-    document.getElementById("content").classList.toggle("sidebar-shown")
-    document.getElementById("toc").classList.toggle("sidebar-shown")
-    sideMenuToggler.classList.toggle("menu-shown")
-  })
+ // show/hide side menu on mobile view
+ const sideMenuToggler = document.getElementById("mobile-sidebar-toggle");
+ sideMenuToggler.addEventListener('click', _e => {
+   document.getElementById("leftColumn").classList.toggle("show")
+   document.getElementById("content").classList.toggle("sidebar-shown")
+   const toc = document.getElementById("toc");
+   if(toc) {
+     toc.classList.toggle("sidebar-shown")
+   }
+   sideMenuToggler.classList.toggle("menu-shown")
+ })
 
     // show/hide mobile menu on mobile view
     const mobileMenuOpenIcon = document.getElementById("mobile-menu-toggle");