Extjs - how to load comboxboxes data before the form data

I have a form that contains several comboxes that their data is coming from the 开发者_运维百科server.

I need to load all of the combobox's data before the form data is loading (from the server).

If Extjs had allow synchronized requests, I would make every combo as synchronized, and after that loading the form data.

but as far as i know, everything needs to be done via callbacks, which makes the form a bit "re-use-less"

Any idea how to salve it? Just to make it clear, I am talking about a situation of editing an employee details for example, which its form data contains:

first_name, last_name, city_id(bombo),country_id(combo) And loading the combobox data of city_id and country_id is critical for the selectedValue issue.

Thanks

combo_store.load();

combo_store.on('load', function(st, records, options)
{
    // callback called after data loading in combo
    // you can load other data
});