HOW TO VALIDATE TEXTBOX INSIDE GRIDVIEW FOOTER TEMPLATE USING JAVASCRIPT

HOW TO VALIDATE TEXTBOX INSIDE GRIDVIEW FOOTER TEMPLATE USING JAVASCRIPT

 <script type="text/javascript">

      function NotAllow(txtAddname) {


          if (document.getElementById(txtAddname).value.length > 16) {
              alert("Please enter less than 16 characters")
          }
          var iChars = "!@#$%^&*()+=-[]\\\';,./{}|\":<>? ";

          for (var i = 0; i <document.getElementById(txtAddname).value.length; i++) {
              if (iChars.indexOf(document.getElementById(txtAddname).value.charAt(i)) != -1) {
                  alert("Your username has special characters. \nThese are not allowed.\n Please remove them and try again.");
                  return false;
              }
          }
      }    

</script>


FIND CONTROL AND USE CONTROL.ATTRIBUTES ADD(  ) FUNCTION

public void BindGrid()
    {   
        dt = new DataTable();
        adap = new SqlDataAdapter("usp_select", con);
        adap.Fill(dt);   
        GridView1.DataSource = dt;
        GridView1.DataBind();
        Button btnAdd = (this.GridView1.FooterRow.FindControl("btnAddRecord") as Button);
        btnAdd.Attributes.Add("onclick", "return NotAllow('" + this.GridView1.FooterRow.FindControl("txtAddname").ClientID + "')");
        con.Close();
    }


protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName.Equals("Add"))
        {
           TextBox txtname =(TextBox)GridView1.FooterRow.FindControl("txtAddname");
           TextBox txtsal = (TextBox)GridView1.FooterRow.FindControl("txtAddsal");
           string name, sal;
           name = txtname.Text;
           sal = txtsal.Text;

           AddEmployee(name, sal);
           GridView1.EditIndex = -1;
                  
           BindGrid();

        }
    }