Reloading data in combo

I have a combo box initialized with an url, i want to reload data when user clicks a button, is there any way to reload it via ajax?

Combo box is the mix of input area and popup list

If you have combo as

{ view:"combo", id:'someField'...

you can access list of options as

var list = $$("someField_list");
after that you can use any list related api

list.clearAll(); list.load("newdata.json");