I think you can do something like this :
config.cm = new Ext.grid.ColumnModel({
defaults:{
sortable: true
},
columns : [{
{
header: 'date',
dataIndex: 'time',
editable:'false',
renderer: formatDate
}]
});
function formatDate(value){
return value ? value.dateFormat('M d, Y') : '';
}
Hopefully that helps you!