Checking email availability with VB.NET WebMethod + JSON + CustomValidator

Question

I've read several posts about this issue (here and in other sites) but no one is working for me. I'm trying to check if a given email is already registered in a database during the register process.

I've a page called Register.aspx in which I've declared the follow JavaScript function:

function check_email_availability(src, args) {
  $.ajax({
    type: "POST",
    async: false,
    timeout: 500,
    contentType: "application/json",
    url: "Register.aspx/CheckEmailAvailability",
    data: "{ 'email' : '" + args.Value + "' }",
    success: function (result) {
      args.IsValid = result.d;
    }
  });
}

In the other hand, in the code behind in Register.aspx.vb, I've the follow WebMethod:

<System.Web.Services.WebMethod()> _
Public Shared Functiion CheckEmailAvailability(ByVal email As String) As String
  If Membership.GetUser(email) Is Nothing Then
    Return "True"
  Else
    Return "False"
End Function

I'm trying to launch the JavaScript function through a CustomValidator but I receive from Chrome's Console the follow message:

Uncaught TypeError: Cannot read property 'Value' of undefined

The error appears right in the line

data: "{ 'email' : '" + args.Value + "' }",

so -always using Chrome-, I've set a breakpoint on that line and, from Console, I've write

args.Value

and I've obtained the correct value, i.e., the email address that I had entered. So... I'm a little lost.

I appreciate any help.

Instead of evaluating in the console (which could have multiple contexts), try highlighting that expression and putting a watch on it. — Steve Campbell
– Steve Campbell, Commented Sep 26, 2012 at 18:01

Community · Accepted Answer · 2017-05-23 12:29:21Z

Well, I finally made it work. I share here the used code. To get into context, in the user registration process, I want to check the email availability.

In the head of Register.aspx:

<script type="text/javascript">
  function check_email_availability(src, args) {
    var isValid;
    $.ajax({
      type: "POST",
      url: "Register.aspx/CheckEmailAvailability",
      timeout: 500,
      data: "{'email' : '" + args.Value + "'}",
      contentType: "application/json; charset=utf-8",
      async: false,
      success: function (result) {
                 isValid = result.d;
               }
    });
    args.IsValid = isValid;
  }
</script>

In the body of Register.aspx:

<asp:TextBox ID="tbEmail" runat="server" CssClass="TextBox" ClientIDMode="Static" TabIndex="1" />
<asp:CustomValidator ID="CValidatorEmail" runat="server" ControlToValidate="tbEmail" ValidateEmptyText="false" ClientValidationFunction="check_email_availability" ErrorMessage="Email already in use" SetFocusOnError="True" />

In the codebehind (Register.aspx.vb):

<System.Web.Services.WebMethod()> _
Public Shared Function CheckEmailAvailability(ByVal email As String) As Boolean
    Dim oMU As MembershipUser = Membership.GetUser(email)
    If oMU IsNot Nothing Then Return False Else Return True
End Function

I hope this will be useful to someone. There is a question almost identical using C# that have help me to make it work.

Regards,

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