From 0c32920a82a00a6f338a021a0e17dd5e1c7809f8 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Thu, 25 Jun 2020 23:43:30 +0200
Subject: [PATCH] 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: https://github.com/nodejs/node/pull/34056
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 lib/internal/event_target.js                 |  2 +-
 test/parallel/test-eventtarget-once-twice.js | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 test/parallel/test-eventtarget-once-twice.js

diff --git a/lib/internal/event_target.js b/lib/internal/event_target.js
index 35d9e7275af2d0..983e2671b7bb6e 100644
--- a/lib/internal/event_target.js
+++ b/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)) {
diff --git a/test/parallel/test-eventtarget-once-twice.js b/test/parallel/test-eventtarget-once-twice.js
new file mode 100644
index 00000000000000..6a38b80e2db75a
--- /dev/null
+++ b/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'));
+});