events: fix add-remove-add case in EventTarget

Make sure that listeners are added properly if there has previously
been one but currently are none for a given event type.

PR-URL: #34056
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

Author: addaleax

lib/internal/event_target.js

@@ -240,7 +240,7 @@ class EventTarget {
     }
 
     let handler = root.next;
-    let previous;
+    let previous = root;
 
     // We have to walk the linked list to see if we have a match
     while (handler !== undefined && !handler.same(listener, capture)) {

test/parallel/test-eventtarget-once-twice.js

@@ -0,0 +1,19 @@
+// Flags: --expose-internals --no-warnings
+'use strict';
+const common = require('../common');
+const {
+  Event,
+  EventTarget,
+} = require('internal/event_target');
+const { once } = require('events');
+
+const et = new EventTarget();
+(async function() {
+  await once(et, 'foo');
+  await once(et, 'foo');
+})().then(common.mustCall());
+
+et.dispatchEvent(new Event('foo'));
+setImmediate(() => {
+  et.dispatchEvent(new Event('foo'));
+});