Using Ajax with WCF and CORS enabled.

[sapator]

Had a lot of trouble configuring this so I am writing it out in case anyone wants to do the same.
This is a WCF - POST-GET enabled WCF service app that will be called through Ajax - Json. This requires to have CORS enabled , so this is the "simplest" example , without having to overload CustomHeaderMessageInspector and EnableCrossOriginResourceSharingBehavior. I am not sure if this will work in another domain as I have only tested locally on Local IIS and Cassini. Should work but then again...WCF...

So here is the service:
Global.asax:

Imports System.Web.SessionState

Public Class Global_asax
    Inherits System.Web.HttpApplication

    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the application is started
    End Sub

    Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the session is started
    End Sub

    Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*")
        If HttpContext.Current.Request.HttpMethod = "OPTIONS" Then
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "POST, PUT, DELETE")

            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept")
            HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000")
            HttpContext.Current.Response.End()
        End If
        ' Fires at the beginning of each request
    End Sub

    Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires upon attempting to authenticate the use
    End Sub

    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when an error occurs
    End Sub

    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the session ends
    End Sub

    Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the application ends
    End Sub

End Class

web.config:

<?xml version="1.0"?>
<configuration>

  <system.web>
    <compilation debug="true" targetFramework="4.0" />
  </system.web>
  <system.serviceModel>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" aspNetCompatibilityEnabled="true" />
    <services>
      <service behaviorConfiguration="Default" name="WcfService1.Service1">
        <endpoint address="" behaviorConfiguration="webBehavior" binding="webHttpBinding" contract="WcfService1.IService1" />
        <endpoint contract="IMetadataExchange" binding="mexHttpBinding" address="mex" />
      </service>
    </services>
    <behaviors>

      <endpointBehaviors>
        <behavior name="webBehavior">
          <webHttp helpEnabled="true" />
        </behavior>
      </endpointBehaviors>

      <serviceBehaviors>
        <behavior name="Default">
          <serviceMetadata httpGetEnabled="true" />
        </behavior>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>      
      </serviceBehaviors>
    </behaviors>
 
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>   
  </system.webServer>

</configuration>

Iservice1:

' NOTE: You can use the "Rename" command on the context menu to change the interface name "IService1" in both code and config file together.
<System.Web.Script.Services.ScriptService()> _
<ServiceContract()>
Public Interface IService1


    ' TODO: Add your service operations here
    <OperationContract()>
    Function GetMedicalHistory() As String

End Interface

' Use a data contract as illustrated in the sample below to add composite types to service operations.

Service1.vb

Imports System.ServiceModel.Activation

' NOTE: You can use the "Rename" command on the context menu to change the class name "Service1" in code, svc and config file together.
<AspNetCompatibilityRequirements(RequirementsMode:=AspNetCompatibilityRequirementsMode.Allowed)> _
Public Class Service1
    Implements IService1

    ' Public Sub New()
    ' End Sub



    <WebInvoke(Method:="POST", RequestFormat:=WebMessageFormat.Json, ResponseFormat:=WebMessageFormat.Json, UriTemplate:="/GetMedicalHistory")>
    Function GetMedicalHistory() As String Implements IService1.GetMedicalHistory      
        Return "x"
    End Function
End Class

....
Create a asp.net project and change the localhost in whatever is correct.

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script src="javascript/jquery-1.11.2.min.js" type="text/javascript"></script>
     <script type="text/javascript">
         $(document).ready(function () {
             getMedicalHistory();
         });

         function getMedicalHistory() {          

             $.ajax({
                 url: 'http://localhost:45156/Service1.svc/GetMedicalHistory',
                 // of 'http://localhost/WcfService1/service1.svc/GetMedicalHistory' // for Local IIS
                 type: 'POST',
                 data: '{}',
                 dataType: 'json',
                 contentType: "application/json; charset=utf-8",
                 success: function (res) {
                     alert('d');
                     console.log("Success");
                     console.log(res);
                     $('#result').html(res.d);
                 },
                 error: function (res) {
                     alert(res);
                     console.log("Error! " + res.statusText);
                 }
             });
         }
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    </div>
    </form>
</body>
</html>

Note this is a simple Ajax call just to see that your WCF breakpoint is hit and running and an alert to see that actually goes to function success, you won't get any data, you need to set up your Ajax and WCF service properly afterwards.