how to preselect a first item in a dropdown

[debutant_ISC]

hi,
(i'm a beginner )
can you tell me how can i preselect a first item in my dropdown

here is the code of a dropdown:

 
{name:"r_customer_name", title:"<b><span style='color: orange'>Client </span></b>", editorType:"select",  optionDataSource:"cs_customers",  
    					changed: function(){
    						var CustomerName = CS_CustomersList.getValue("r_customer_name");
    						CS_CustomerID = CustomersResultSet.data.find({r_customer_name : CustomerName}).r_customer_idnum; 
    						CS_ServicesTreeGrid.setCriteria({r_service_fk_customer_idnum :CS_CustomerID }); 
    						CS_OrderViewList.fetchData({r_customer_idnum :CS_CustomerID }); 
    						NewCar_CustomerID = CS_CustomerID;
    					}
    }

I found a function selectRecord() but it works only for a listgrid.