Retrieve and set LookUp value in MS CRM

Set Lookup value

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var BUlookupVal = new Array();                      

      BUlookupVal[0] = new Object();

      BUlookupVal[0].id = GUID;

      BUlookupVal[0].name = Value;

      BUlookupVal[0].entityType =_entity logical name;                       

Xrm.Page.getAttribute("fieldname").setValue(BUlookupVal);

Retrieve Lookup Value

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var LKName = Xrm.Page.getAttribute("Lookup_fieldname").getValue();

 var LkId = LKName .id;

var LKname = LKName.name;

var LKtype = LKName.entitytype;