Use default `closest` if available!

app/assets/javascripts/extensions/element.js.es6

@@ -3,7 +3,7 @@
 
 Element.prototype.matches = Element.prototype.matches || Element.prototype.msMatchesSelector;
 
-Element.prototype.closest = function closest(selector, selectedElement = this) {
+Element.prototype.closest = Element.prototype.closest || function closest(selector, selectedElement = this) {
   if (!selectedElement) return;
   return selectedElement.matches(selector) ? selectedElement : Element.prototype.closest(selector, selectedElement.parentElement);
 };