Masterspreads

     // lets create some master spreads
    var doc = app.documents.add();
      var master_spread1_pg1 = doc.masterSpreads.item(0).pages.item(0);// edit the master spreads
       
          master_spread1_pg1.marginPreferences.properties = {
              right: 12.7,
              top:12.7 ,
              left:12.7 ,
              bottom:12.7,
              columnGutter:5,
          };  
      
      var master_spread1_pg2 = doc.masterSpreads.item(0).pages.item(1);//edit the other master spread
      
          master_spread1_pg2.marginPreferences.properties = {
              right: 12.7,
              top:12.7 ,
              left:12.7 ,
              bottom:12.7,
              columnGutter:5,
          };  
      
    master_spread1_pg1.marginPreferences.columnCount = 5;
    master_spread1_pg2.marginPreferences.columnCount = 5;
    var my_spread = doc.masterSpreads.item(0);
    doc.pages.item(0).appliedMaster = my_spread;