events: getMaxListeners detects 0 listeners

PR-URL: #56807
Refs: nodejs/undici#4032
Refs: c1ccade
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Yagiz Nizipli <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Juan José Arboleda <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Chemi Atlow <[email protected]>

Author: KhafraDev

lib/events.js

@@ -939,7 +939,7 @@ function getEventListeners(emitterOrTarget, type) {
 function getMaxListeners(emitterOrTarget) {
   if (typeof emitterOrTarget?.getMaxListeners === 'function') {
     return _getMaxListeners(emitterOrTarget);
-  } else if (emitterOrTarget?.[kMaxEventTargetListeners]) {
+  } else if (typeof emitterOrTarget?.[kMaxEventTargetListeners] === 'number') {
     return emitterOrTarget[kMaxEventTargetListeners];
   }
 

test/parallel/test-events-getmaxlisteners.js

@@ -17,3 +17,8 @@ const { getMaxListeners, EventEmitter, defaultMaxListeners, setMaxListeners } =
   setMaxListeners(101, et);
   assert.strictEqual(getMaxListeners(et), 101);
 }
+
+{
+  const ac = new AbortController();
+  assert.strictEqual(getMaxListeners(ac.signal), 0);
+}