events: allow dispatch many times without listener

Fast path for EventTarget dispatch with no listeners didn't reset
kIsBeingDispatched flag, meaning same event couldn't be dispatched
multiple times.

PR-URL: #39772
Refs: #39395
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>

Author: mrbbot

lib/internal/event_target.js

@@ -521,8 +521,11 @@ class EventTarget {
     }
 
     const root = this[kEvents].get(type);
-    if (root === undefined || root.next === undefined)
+    if (root === undefined || root.next === undefined) {
+      if (event !== undefined)
+        event[kIsBeingDispatched] = false;
       return true;
+    }
 
     let handler = root.next;
     let next;

test/parallel/test-eventtarget.js

@@ -186,6 +186,22 @@ let asyncTest = Promise.resolve();
   deepStrictEqual(event.composedPath(), []);
 
 
+  eventTarget2.dispatchEvent(event);
+  strictEqual(event.eventPhase, Event.NONE);
+  strictEqual(event.target, eventTarget2);
+  deepStrictEqual(event.composedPath(), []);
+}
+{
+  // Same event dispatched multiple times, without listeners added.
+  const event = new Event('foo');
+  const eventTarget1 = new EventTarget();
+  const eventTarget2 = new EventTarget();
+
+  eventTarget1.dispatchEvent(event);
+  strictEqual(event.eventPhase, Event.NONE);
+  strictEqual(event.target, eventTarget1);
+  deepStrictEqual(event.composedPath(), []);
+
   eventTarget2.dispatchEvent(event);
   strictEqual(event.eventPhase, Event.NONE);
   strictEqual(event.target, eventTarget2);