Added isElement(), which returns true if the given argument is an HTMLElement.

app/js/common/Utils.js

 const utils = {
+  isElement:function(el){
+    // Code based on...
+    // https://stackoverflow.com/questions/384286/javascript-isdom-how-do-you-check-if-a-javascript-object-is-a-dom-object
+    try {
+      // Using W3 DOM2 (works for FF, Opera and Chrome)
+      return obj instanceof HTMLElement;
+    } catch(e) {
+      // Browsers not supporting W3 DOM2 don't have HTMLElement and
+      // an exception is thrown and we end up here. Testing some
+      // properties that all elements have (works on IE7)
+      return (typeof obj==="object") && 
+        (obj.nodeType===1) && 
+        (typeof obj.style === "object") &&
+        (typeof obj.ownerDocument ==="object");
+      }
+  },
+
   debounce:function(func, delay){
     var timeout = null;
     return function(){