Replacing JavaScipt
//===================
<script type ="text/javascript" >
function dateSelectionChanged(sender, args) {
var dt1 = sender.get_selectedDate();
dt1.setMonth(dt1.getMonth() + 5);
var dt2 = dt1.format("dd, MM , yyyy");
document.getElementById('TextBox1').value = dt2;
}
</script>