Synchronous PageMethod Custom Validator Control

Add this property:

public bool DebugScript
        {
            get
            {
                 return (this.ViewState["PMWebMethodDebugMode"]!=null) ? (bool)this.ViewState["PMWebMethodDebugMode"] : false;
            }
            set
            {
                this.ViewState["PMWebMethodDebugMode"] = value;
            }
        }

debugger

function BrkeyCustomValidator_Validate(source, args)
{
PageMethods.set_path('CreateBridgeDialogMC.aspx');
   var url = PageMethods.get_path() + '/' + 'CheckIfBrkeyExists';
   var resp = GetSynchronousJSONResponse(url, '{"theBrkey":"'+args.Value+'"}');
   var result =  JSON.parse(resp);
   args.IsValid = result.d;
}

Add this property:

/// <summary>
       ///  so the name of the argument to the Webmethod can be set in the designer.  Defaults to 'value'
       /// </summary>
       public string WebMethodParameterName
       {
           get
           {
               return (string)this.ViewState["PMWebMethodParameterName"] ?? String.Empty; // was never provided
           }
           set
           {
               this.ViewState["PMWebMethodParameterName"] = (value == null) ? "value" : value;
           }
       }

String funcs = "\n" +
                   ((DebugScript) ? "debugger\n" : "\n") +
                    "function " + ClientID + "_Validate(source, args)\n" +

                    "{\nPageMethods.set_path('" + GetPage() + "');\n" +
                    (String.IsNullOrEmpty(WebMethodRunCondition) ? String.Empty :
                    "	if(" + WebMethodRunCondition + "){\n\t") +
                    "   var url = PageMethods.get_path() + '/' + '" + WebMethod + "';\n" +
                    "   var resp = GetSynchronousJSONResponse(url, '{\"" + WebMethodParameterName + "\":\"'+args.Value+'\"}');\n" +
                    //"   var result =  JSON.parse(eval('('+resp+')'));\n" +
                    "   var result =  JSON.parse(resp);\n" +
                    "   args.IsValid = result.d;\n" +
                     (String.IsNullOrEmpty(WebMethodRunCondition) ? String.Empty :
                    "	}\n") +
                    "}";
                // the var result is an object, not a simple type.
                // must be parsed to extract boolean 
                // see example here http://stackoverflow.com/questions/24546483/how-to-get-data-field-from-xhr-responsetext
                Page.ClientScript.RegisterClientScriptBlock(GetType(), ClientID + "_Scripts", funcs, true);

Environment

Observation

"//   var result =  JSON.parse(eval('('+resp+')'));\n" +
                    "   var result =  JSON.parse(resp);\n" +
                    "   args.IsValid = result.d;\n" +
                     (String.IsNullOrEmpty(WebMethodRunCondition) ? String.Empty :
                    "	}\n") +
                    "}";
                // the var result is an object, not a simple type.
                // must be parsed to extract boolean 
                // see example here http://stackoverflow.com/questions/24546483/how-to-get-data-field-from-xhr-responsetext

using (var dbContext = _context.CreateUnitOfWork())
                {
                    var qry = from b in dbContext.Bridges
                              where b.Id == theBrkey
                              select b;


                    var hits = qry.Count<Bridge>();

                    result = (hits == 0);

                }

{object d: false} 

eval('('+resp+')')