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?

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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',
    ...
});