date textbox validation using javascript

protected string CheckDateErrors(string dateGiven)
       {
           // let's make sure that the date entered by user
           // does not exceed the present date or goes back
           // over a year.
           // we need to try parse!
           DateTime userDate = DateTime.Parse(dateGiven);
           //DateTime userDate;

           int userYear = userDate.Year;
           int userMonth = userDate.Month;
           int userDay = userDate.Day;

           // not valid! user entered future date, can't allow this to happen
           if (userDate.CompareTo(DateTime.Now) > 0)
           {
               //this.tbBeginDate.ForeColor = Color.Red;
               //this.tbBeginDate.BorderColor = Color.Red;
               return "* Cannot Enter Future Dates;";
           }
           // date cannot be more than one year old.
           else if (userDate.CompareTo(DateTime.Now) <= 0)
           {
               int difference = DateTime.Today.Year - userYear;


               // going too far back; now allowed.
               if (userYear < (DateTime.Today.Year - 1))
               {
                   return "* Cannot Enter Past One Year: Compared Years;";
               }
               else if ((difference == 1) &&
                   (userMonth < DateTime.Today.Month))
               {
                   return "* Cannot Enter Past One Year: Compared Months;";
               }
               else if ((difference == 1) &&
                    (userMonth >= DateTime.Today.Month) &&
                    (userDay < DateTime.Today.Day))
               {
                   return "* Cannot Enter Past One Year: Compared Days";
               }
               return "none";
           }
           return "none";
       }