How to calculate current age from Date of Birth using Javascript in Dynamics CRM 2011

function CalculateAge()

    {

    if(Xrm.Page.getAttribute("birthdate").getValue() != null)

    {

           var currentdate = new Date();

           var birthdate = Xrm.Page.getAttribute("birthdate").getValue();

           var monthdiff = currentdate.getMonth() - birthdate.getMonth();          

       var currentage;

 

           if(monthdiff > -1)

           {

        currentage = currentdate.getFullYear() - birthdate.getFullYear();                    

                Xrm.Page.getAttribute("new_currentage").setValue(currentage);

           }

           else

           {

        currentage = currentdate.getFullYear() - birthdate.getFullYear() - 1

                Xrm.Page.getAttribute("new_currentage").setValue(currentage);

           }

    }

    }