make event handler validation private

src/canvasdrawer.js

@@ -65,6 +65,11 @@ class CanvasDrawer extends $.DrawerBase{
         // Canvas default is "true", so this will only be changed if user specifies "false" in the options or via setImageSmoothinEnabled.
         this._imageSmoothingEnabled = true;
 
+
+        // Since the tile-drawn and tile-drawing events are fired by this drawer, make sure handlers can be added for them
+        this.viewer.allowEventHandler("tile-drawn");
+        this.viewer.allowEventHandler("tile-drawing");
+
     }
 
     /**

src/eventsource.js

@@ -51,7 +51,7 @@
  */
 $.EventSource = function() {
     this.events = {};
-    this.rejectedEventList = {};
+    this._rejectedEventList = {};
 };
 
 /** @lends OpenSeadragon.EventSource.prototype */
@@ -95,8 +95,8 @@ $.EventSource.prototype = {
      */
     addHandler: function ( eventName, handler, userData, priority ) {
 
-        if(Object.prototype.hasOwnProperty.call(this.rejectedEventList, eventName)){
-            $.console.error(`Error adding handler for ${eventName}. ${this.rejectedEventList[eventName]}`);
+        if(Object.prototype.hasOwnProperty.call(this._rejectedEventList, eventName)){
+            $.console.error(`Error adding handler for ${eventName}. ${this._rejectedEventList[eventName]}`);
             return false;
         }
 
@@ -217,9 +217,20 @@ $.EventSource.prototype = {
      * to be printed to the console
      * @param {String} eventName - Name of the event
      * @param {String} [errorMessage] - Optional string to print to the console
+     * @private
      */
     rejectEventHandler(eventName, errorMessage = ''){
-        this.rejectedEventList[eventName] = errorMessage;
+        this._rejectedEventList[eventName] = errorMessage;
+    },
+
+    /**
+     * Explicitly allow an event handler to be added for this event type, undoing
+     * the effects of rejectEventHandler
+     * @param {String} eventName - Name of the event
+     * @private
+     */
+    allowEventHandler(eventName){
+        delete this._rejectedEventList[eventName];
     }
 
 };

src/htmldrawer.js

@@ -51,6 +51,8 @@ class HTMLDrawer extends $.DrawerBase{
 
         // Reject listening for the tile-drawing event, which this drawer does not fire
         this.viewer.rejectEventHandler("tile-drawing", "The HTMLDrawer does not raise the tile-drawing event");
+        // Since the tile-drawn event is fired by this drawer, make sure handlers can be added for it
+        this.viewer.allowEventHandler("tile-drawn");
     }
 
     /**