ASP.NET AJAX C# Handlers + typeahead.js plugin for autocomplete (i don't want use jquery autocomplete!!)

Hi, i have this code in javascript that call 2 function handlers written in c#:

var substringMatcher = function (strs) {
            return function findMatches(q, cb) {
                var matches, substringRegex;

                // an array that will be populated with substring matches
                matches = [];

                // regex used to determine if a string contains the substring `q`
                substrRegex = new RegExp(q, 'i');

                // iterate through the pool of strings and for any string that
                // contains the substring `q`, add it to the `matches` array
                $.each(strs, function (i, str) {
                    if (substrRegex.test(str)) {
                        matches.push(str);
                    }
                });

                cb(matches);
            };
        };

        var nomiClienti; //= ['Cristian', 'Luigi', '...'];
        var nomiOperatori; //= ['Operatore1', 'Operatore2', 'Operatore3'];


        $.ajax({
            url: "../../handlers/caricaListaNomiClienti.ashx",
            type: "GET",
            dataType: "json",
            error: function (data) {
                alert("Errore durante il caricamento dei nomi dei clienti: " + data);
            },
            success: function (data) {
                console.log(data);
                alert(data);
                nomiClienti = data;
            }
        })$.ajax({
            url: "../../handlers/caricaListaNomiOperatori.ashx",
            type: "GET",
            dataType: "json",
            error: function (data) {
                alert("Errore durante il caricamento dei nomi degli operatori: " + data);
            },
            success: function (data) {
                console.log(data);
                alert(data);
                nomiOperatori = data;
            }
        })$('.typeahead').typeahead({
            hint: true,
            highlight: true,
            minLength:3 
        },
{
    name: 'nomiClienti',
    source: substringMatcher(nomiClienti)
});$('.typeahead2').typeahead({
    hint: true,
    highlight: true,
    minLength: 3
},
{
    name: 'nomiOperatori',
    source: substringMatcher(nomiOperatori)
});

C# Function Handler caericaListaNomiOperatori.ashx.cs

public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";

            try
            {
                using (DatabaseDataContext contestoDB = new DatabaseDataContext())
                { 
                    var elencoClienti = (from db in contestoDB.Utenti
                                         where db.IDGruppo == 2
                                         select db.Nome).Distinct();
                     
                    context.Response.Write(JsonConvert.SerializeObject(elencoClienti.ToArray()));
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            context.Response.Write(null);
        }

C# Function Handler caericaListaNomiClienti.ashx.cs

 public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";

            try
            {
                using (DatabaseDataContext contestoDB = new DatabaseDataContext())
                {
                    var elencoClienti = (from db in contestoDB.Clienti 
                                         select db.Nome).Distinct();

                    context.Response.Write(JsonConvert.SerializeObject(elencoClienti.ToArray()));
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            context.Response.Write(null);
        }

Ok. I want that handlers give me array in data (response inside ajax call) in this format for loading source of typeahead plugin.

var nomiOperatori = ["asdxxxx", "asdxxxx", "asdxxxx"]; //handler response 1

var nomiClienti = ["Tizio", "Caio", "Luca"]; //handler response 2

But when i write 3rd letter this ******** appears:

Uncaught TypeError: Cannot read property 'length' of undefined

Why?

I need a solution for this morning!!! Help me please!!!

Thanks!!

Cris