How to get value from store and use it outside callback

i cannot get value from callback

please help

Code:

var m_Warehouse=Ext.create('Ext.data.Store',{model:'s_autorefill',autoLoad: true, storeId: 'm_Warehouse',proxy:{type:'ajax',url:'desktop/stock_listcombo/warehouse',reader:{root:'data',type: 'json',idProperty:'idx'}}});




m_Warehouse.load(
{
callback : function(e){
result = e[0].get('idx')


}
}
);

var myread = 'desktop/stock_listproduct/prod_modeltype-1/prod_stockstatus-1-' +  result ;