events: add hasEventListener util for validate

sungpaks · marco-ippolito · commit e87db6c9bcae · 2025-03-06T13:38:01.000+01:00
There was some repetitive logics that validated the existence of eventlisteners. We now replace this with a single line of, `hasEventListener(self, type)`. `self` is the object(e.g. EventEmitter) to be checked whether eventlisteners exists or not. `type` is the type of eventlisteners, which can be `undefined` PR-URL: #55230 Reviewed-By: Jason Zhang <xzha4350@gmail.com>
diff --git a/lib/events.js b/lib/events.js
@@ -287,6 +287,12 @@ ObjectDefineProperty(EventEmitter, 'defaultMaxListeners', {
   },
 });
 
+function hasEventListener(self, type) {
+  if (type === undefined)
+    return self._events !== undefined;
+  return self._events !== undefined && self._events[type] !== undefined;
+}
+
 ObjectDefineProperties(EventEmitter, {
   kMaxEventTargetListeners: {
     __proto__: null,
@@ -680,13 +686,11 @@ EventEmitter.prototype.removeListener =
     function removeListener(type, listener) {
       checkListener(listener);
 
-      const events = this._events;
-      if (events === undefined)
+      if (!hasEventListener(this, type))
         return this;
 
+      const events = this._events;
       const list = events[type];
-      if (list === undefined)
-        return this;
 
       if (list === listener || list.listener === listener) {
         this._eventsCount -= 1;
@@ -742,9 +746,9 @@ EventEmitter.prototype.off = EventEmitter.prototype.removeListener;
  */
 EventEmitter.prototype.removeAllListeners =
     function removeAllListeners(type) {
-      const events = this._events;
-      if (events === undefined)
+      if (!hasEventListener(this))
         return this;
+      const events = this._events;
 
       // Not listening for removeListener, no need to emit
       if (events.removeListener === undefined) {
@@ -789,14 +793,10 @@ EventEmitter.prototype.removeAllListeners =
     };
 
 function _listeners(target, type, unwrap) {
-  const events = target._events;
-
-  if (events === undefined)
+  if (!hasEventListener(target, type))
     return [];
 
-  const evlistener = events[type];
-  if (evlistener === undefined)
-    return [];
+  const evlistener = target._events[type];
 
   if (typeof evlistener === 'function')
     return unwrap ? [evlistener.listener || evlistener] : [evlistener];
