Private Sub Worksheet_Change(ByVal Target As Range)
    Dim rc As Range
    Select Case Target.Address(0, 0)
    Case "A1"
        Set rc = Range("B1")
    Case "B1"
        Set rc = Range("A1")
    End Select
    Application.EnableEvents = 0
    rc.Value = Target.Value
    Application.EnableEvents = 1
End Sub

function onEdit(e) {  
  var actRng = e.range;
  var sheet = e.source;
  var row =   actRng.getRow();
  var column = actRng.getColumn();


  if (row = 1) {
    if (column < 3)
    {
    if (column == 1){sheet.getRange("B1").setValue(e.value);}
    else {sheet.getRange("A1").setValue(e.value);}
    }
  }
}