Avoid search prototype chain (#2019)

1 files changed, 3 insertions, 3 deletions

diff --git a/js/event_target.ts b/js/event_target.ts
index 98b7bbcb8..52e52b03a 100644
--- a/js/event_target.ts
+++ b/js/event_target.ts
@@ -14,7 +14,7 @@ export class EventTarget implements domTypes.EventTarget {
     listener: domTypes.EventListenerOrEventListenerObject | null,
     _options?: boolean | domTypes.AddEventListenerOptions
   ): void {
-    if (!(type in this.listeners)) {
+    if (!this.listeners.hasOwnProperty(type)) {
       this.listeners[type] = [];
     }
     if (listener !== null) {
@@ -27,7 +27,7 @@ export class EventTarget implements domTypes.EventTarget {
     callback: domTypes.EventListenerOrEventListenerObject | null,
     _options?: domTypes.EventListenerOptions | boolean
   ): void {
-    if (type in this.listeners && callback !== null) {
+    if (this.listeners.hasOwnProperty(type) && callback !== null) {
       this.listeners[type] = this.listeners[type].filter(
         listener => listener !== callback
       );
@@ -35,7 +35,7 @@ export class EventTarget implements domTypes.EventTarget {
   }
 
   public dispatchEvent(event: domTypes.Event): boolean {
-    if (!(event.type in this.listeners)) {
+    if (!this.listeners.hasOwnProperty(event.type)) {
       return true;
     }
     const stack = this.listeners[event.type].slice();