This event executes callback function each time when product option was changed. The callback functions accept one parameter: productid, specifying ID of the product changed. OnProductOptionsChanged works for following options type: dropdown list, radio button and checkbox. Input, textarea and upload files types are not supported yet.

Show an alert if product options were changed:

Ecwid.OnProductOptionsChanged.add(function(productid) {
   window.alert("Options changed, product id:" + productid);