Auto popluate Optionset field value

function optionsetDetails()
{
var contName=Xrm.Page.getAttribute("new_contnew").getValue();

if (contName != null) {
         var contId = contName[0].id;
     }
	 
	 var serverUrl=Xrm.Page.context.getClientUrl();
    var oDataSelect=serverUrl+"/XRMServices/2011/OrganizationData.svc/new_contSet?$select=new_InterpreterType&$filter=new_lapinterpreterId eq guid'"+contId+"'";

	var retrieveReq=new XMLHttpRequest();
    retrieveReq.open("GET", encodeURI(oDataSelect), false);
    retrieveReq.setRequestHeader("Accept", "application/json");
    retrieveReq.setRequestHeader("Content-Type", "application/json;charset=utf-8");
    retrieveReq.send();
            if (retrieveReq.status === 200) {
                var retrieved = JSON.parse(retrieveReq.responseText).d;
				
if (retrieved != null && retrieved.results.length > 0) 
                {
				   var interpretertype=retrieved.results[0].new_InterpreterType;        
                   SetOptionSetValue("new_interpretertype",interpretertype);				   
				}
 
}
}
function SetOptionSetValue(optionsetAttribute,optionValue)
{
var options=Xrm.Page.getAttribute(optionsetAttribute).getOptions();
for(var i in options)
{
alert(options[i].value);
if(options[i].value==optionValue)
{
Xrm.Page.getAttribute(optionsetAttribute).setValue(options[i].value);
}
}
}