Posted by Sean P. DeNigris on Feb 18, 2014; 10:34pm
URL: https://forum.world.st/Prototyping-DND-tp4744713p4744730.html

Tim Felgentreff-2 wrote

If you override dropOn, you need to use $super(evt) to call into the
original method.

Ahh, thank you. That did it:
this.addScript(function dropOn(morph) {
    alert('do this first');
    return $super(morph)
}).tag([]);