Added event parameter,

dist/iwmlib.pixi.js

@@ -6042,6 +6042,8 @@
         onMouseWheel(event) {
             if (this.capture(event) && this.target.onMouseWheel) {
                 this.target.onMouseWheel(event);
+            } else {
+                //console.warn('Target has no onMouseWheel callback')
             }
         }
 
@@ -6251,6 +6253,8 @@
                 }
                 if (this.target.onMouseWheel) {
                     this.target.onMouseWheel(event);
+                } else {
+                    //console.warn('Target has no onMouseWheel callback', this.target)
                 }
             }
         }