Please override the 'clear' method of combobox. When calling the 'clear' method. The 'onClear' event fires.
(function(){
var clear = $.fn.combobox.methods.clear;
$.extend($.fn.combobox.methods, {
clear: function(jq){
return jq.each(function(){
clear.call($.fn.combobox.methods, $(this));
var opts = $(this).combobox('options');
if (opts.onClear){
opts.onClear.call(this);
}
})
}
})
})(jQuery);