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 <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: mrbbot

lib/internal/event_target.js

@@ -521,8 +521,11 @@ class EventTarget {
 }
 
 constroot=this[kEvents].get(type);
-if(root===undefined||root.next===undefined)
+if(root===undefined||root.next===undefined){
+if(event!==undefined)
+event[kIsBeingDispatched]=false;
 returntrue;
+}
 
 lethandler=root.next;
 letnext;

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.
+constevent=newEvent('foo');
+consteventTarget1=newEventTarget();
+consteventTarget2=newEventTarget();
+
+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);