var mailingLists = (function (requestCompleted) {
    var endpointUrl = "http://localhost:59688/api/mailinglists/";
    var userId = "a60ff43a-b844-4162-9cdd-3fd67d82975a";
    var apiKey = "cf5f31ef-e765-4c6c-9386-6bafc48b06ab";


    return $.ajax({
        url: endpointUrl + userId + "/" + apiKey + "?format=json",
        dataType: "json",
        complete: function (data) {
            requestCompleted(requestCompleted);
        }
    });
});

mailingLists(function(data){
   //data.responseText
});