Here is the simple solution to achieve this functionality.
function CB(){
this.ff = [];
this.onSelect = (function(){
var ff = this.ff;
return function(row){
for(var i=0; i<ff.length; i++){
ff[i].call(this,row);
}
}
}).call(this);
};
CB.prototype.add = function(f){
this.ff.push(f);
};
var cb = new CB();
cb.add(function(row){
console.log('function1:'+row);
});
cb.add(function(row){
console.log('function2:'+row);
});
cbo.combobox('options').onSelect = cb.onSelect;