How to set value for extjs combo after combo load?

How to set value for extjs combo a开发者_如何学编程fter combo load?

I have a Country combo (I have bind this json store).

How to set default value as United States?

There is value property for combobox.

If you know the code for the default value you can try using it.

new Ext.form.ComboBox({
    ...
    value: 'US',
    ...
});