watermarking textbox with textmode as password

<script language="javascript" type="text/javascript">
                   function WaterMark(txtName, event) {
                       var defaultText = "Enter Username Here";

                       if (txtName.value.length == 0 & event.type == "blur") {

                           txtName.style.color = "Gray";
                           txtName.value = defaultText;
                           txtName.setAttribute("type", "input");
                       }

                       if (txtName.value == defaultText & event.type == "focus") {
                           txtName.style.color = "black";
                           txtName.value = "";
                       }
                   }

                   function myFunction(txtName, event) {
                       txtName.setAttribute("type", "Password");
                   }
               </script>
               <asp:TextBox ID="txtUserName" runat="server" Text="Enter Username Here" ForeColor="Gray"
                   onblur="WaterMark(this, event);" onfocus="WaterMark(this, event);" onkeypress="myFunction(this, event)" />