change append() to appendChild

Author: rbastiansch

22 - Follow Along Link Highlighter/index-FINISHED.html

@@ -29,7 +29,7 @@
   const triggers = document.querySelectorAll('a');
   const highlight = document.createElement('span');
   highlight.classList.add('highlight');
-  document.body.append(highlight);
+  document.body.appendChild(highlight);
 
   function highlightLink() {
     const linkCoords = this.getBoundingClientRect();