refactoring

more readable and more modern way

Author: lumosmind

1-js/09-classes/07-mixins/article.md

@@ -154,7 +154,7 @@ let eventMixin = {
    *  this.trigger('select', data1, data2);
    */
   trigger(eventName, ...args) {
-    if (!this._eventHandlers || !this._eventHandlers[eventName]) {
+    if (!this._eventHandlers?.[eventName]) {
       return; // no handlers for that event name
     }