ExtJS4 gives an example of the default values in the Combobox Settings list

This is the model

 
Ext.regModel('commemModel', { 
fields : [ 'name', 'id' ] 
}); 

The default value for defining a container with a store setting id s1 is the first quarter

 
var gjcx1 = new Ext.data.Store({ 
autoLoad:true, 
model : commemModel, 
proxy : { 
type : 'ajax', 
url : '../store/cxjd.json' 

}, 
listeners :{ 
load:function(){ 
Ext.getCmp('s1').setValue('q1'); 
} 
} 

}); 

The following is cxjd.json

 
[ 
{name:' In the first quarter ',id:'q1'}, 
{name:' In the second quarter ',id:'q2'}, 
{name:' In the third quarter ',id:'q3'}, 
{name:' In the fourth quarter ',id:'q4'} 
]