Issue #3239507 by hooroomoo, bnjmnm: Add CustomEvent polyfill to support IE11

core/core.libraries.yml

@@ -186,6 +186,11 @@ drupal.collapse:
     - core/drupal.form
     - core/once
 
+drupal.customevent:
+  version: VERSION
+  js:
+    misc/polyfills/customevent.js: { weight: -20 }
+
 drupal.date:
   version: VERSION
   js:

core/misc/cspell/dictionary.txt

@@ -320,6 +320,7 @@ curle
 curlopt
 currenttime
 currentuser
+customevent
 customly
 customrequest
 cweagans

core/misc/polyfills/customevent.es6.js

+/**
+ * @file
+ * Provides a polyfill for CustomEvent.
+ *
+ * This is needed for Internet Explorer 11.
+ *
+ * This has been copied from MDN Web Docs code samples. Code samples in the MDN
+ * Web Docs are licensed under CC0.
+ *
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent#Polyfill
+ * @see https://developer.mozilla.org/en-US/docs/MDN/About#Code_samples_and_snippets
+ */
+// eslint-disable-next-line func-names
+(function () {
+  if (typeof window.CustomEvent === 'function') return false;
+
+  function CustomEvent(event, params) {
+    params = params || { bubbles: false, cancelable: false, detail: null };
+    const evt = document.createEvent('CustomEvent');
+    evt.initCustomEvent(
+      event,
+      params.bubbles,
+      params.cancelable,
+      params.detail,
+    );
+    return evt;
+  }
+
+  window.CustomEvent = CustomEvent;
+})();

core/misc/polyfills/customevent.js

+/**
+* DO NOT EDIT THIS FILE.
+* See the following change record for more information,
+* https://www.drupal.org/node/2815083
+* @preserve
+**/
+
+(function () {
+  if (typeof window.CustomEvent === 'function') return false;
+
+  function CustomEvent(event, params) {
+    params = params || {
+      bubbles: false,
+      cancelable: false,
+      detail: null
+    };
+    var evt = document.createEvent('CustomEvent');
+    evt.initCustomEvent(event, params.bubbles, params.cancelable, params.detail);
+    return evt;
+  }
+
+  window.CustomEvent = CustomEvent;
+})();
\ No newline at end of file