ref(iframe_api): Use EventEmitter

doc/api.md

 ```javascript
 api.executeCommands(commands)
 ```
-The `commands` parameter is an object with the names of the commands as keys and the arguments for the commands asvalues:
+The `commands` parameter is an object with the names of the commands as keys and the arguments for the commands as values:
 ```javascript
 api.executeCommands({displayName: ['nickname'], toggleAudio: []});
 ```
 
 You can add event listeners to the embedded Jitsi Meet using the `addEventListener` method.
+*NOTE: This method still exists but it is deprecated. JitsiMeetExternalAPI class extends [EventEmitter]. Use [EventEmitter] methods (`addListener` or `on`).*
 ```javascript
 api.addEventListener(event, listener)
 ```
 You can also add multiple event listeners by using `addEventListeners`.
 This method requires one argument of type Object. The object argument must
 have the names of the events as keys and the listeners of the events as values.
+*NOTE: This method still exists but it is deprecated. JitsiMeetExternalAPI class extends [EventEmitter]. Use [EventEmitter] methods.*
 
 ```javascript
 function incomingMessageListener(object)
 ```
 
 If you want to remove a listener you can use `removeEventListener` method with argument the name of the event.
-
+*NOTE: This method still exists but it is deprecated. JitsiMeetExternalAPI class extends [EventEmitter]. Use [EventEmitter] methods( `removeListener`).*
 ```javascript
 api.removeEventListener("incomingMessage");
 ```
 
 If you want to remove more than one event you can use `removeEventListeners` method with an Array with the names of the events as an argument.
+*NOTE: This method still exists but it is deprecated. JitsiMeetExternalAPI class extends [EventEmitter]. Use [EventEmitter] methods.*
 ```javascript
 api.removeEventListeners(["incomingMessage", "outgoingMessageListener"]);
 ```
 
 [config.js]: https://github.com/jitsi/jitsi-meet/blob/master/config.js
 [interface_config.js]: https://github.com/jitsi/jitsi-meet/blob/master/interface_config.js
+[EventEmitter]: https://nodejs.org/api/events.html

modules/API/external/external_api.js

 const logger = require("jitsi-meet-logger").getLogger(__filename);
 import postisInit from "postis";
+import EventEmitter from "events";
 
 /**
  * The minimum width for the Jitsi Meet frame
 /**
  * The IFrame API interface class.
  */
-class JitsiMeetExternalAPI {
+class JitsiMeetExternalAPI extends EventEmitter {
     /**
      * Constructs new API instance. Creates iframe element that loads
      * Jitsi Meet.
      */
     constructor(domain, room_name, width, height, parentNode,
         configOverwrite, interfaceConfigOverwrite, noSsl, jwt) {
+        super();
+
         if (!width || width < MIN_WIDTH) {
             width = MIN_WIDTH;
         }
      * readyToClose - all hangup operations are completed and Jitsi Meet is
      * ready to be disposed.
      * @param object
+     *
+     * NOTE: This method is not removed for backward comatability purposes.
      */
     addEventListeners(object) {
         for (var i in object) {
      * }}
      * @param event the name of the event
      * @param listener the listener
+     *
+     * NOTE: This method is not removed for backward comatability purposes.
      */
     addEventListener(event, listener) {
-        if (!(event in events)) {
-            logger.error("Not supported event name.");
-            return;
-        }
-        // We cannot remove listeners from postis that's why we are handling the
-        // callback that way.
-        if (!this.postisListeners[event]) {
-            this.postis.listen(events[event], data => {
-                if((event in this.eventHandlers) &&
-                    typeof this.eventHandlers[event] === "function")
-                    this.eventHandlers[event].call(null, data);
-            });
-            this.postisListeners[event] = true;
-        }
-        this.eventHandlers[event] = listener;
+        this.on(event, listener);
     }
 
     /**
      * Removes event listener.
      * @param event the name of the event.
+     * NOTE: This method is not removed for backward comatability purposes.
      */
     removeEventListener(event) {
-        if(!(event in this.eventHandlers))
-        {
-            logger.error("The event " + event + " is not registered.");
-            return;
-        }
-        delete this.eventHandlers[event];
+        this.removeListeners(event);
     }
 
     /**
      * Removes event listeners.
      * @param events array with the names of the events.
+     * NOTE: This method is not removed for backward comatability purposes.
      */
     removeEventListeners(events) {
         for(var i = 0; i < events.length; i++) {
             changeParticipantNumber.bind(null, this, 1));
         this.postis.listen("participant-left",
             changeParticipantNumber.bind(null, this, -1));
+
+        for (const eventName in events) {
+            const postisMethod = events[eventName];
+            this.postis.listen(postisMethod,
+                (...args) => this.emit(eventName, ...args));
+        }
     }
 
     /**