function AjaxData(getpost, datatype, method, params) {
                var data;

                $.ajax({
                    type: getpost,
                    url: method,
                    contentType: 'application/json; charset=utf-8',
                    dataType: datatype,
                    cache: false,
                    data: params,
                    success: function (dat) {
                        data = dat;
                    },
                    error: function (xhr, ajaxOptions, thrownError) {
                        ShowError(thrownError);
                    }
                });

                return data;
            };

function Test(){
var test = AjaxData("POST", "json", url, "{ 'name':'', 'codeword':'' }");

//for(var t  = 0; t < test.length; t++){

}
}

$.ajax({
                    type: getpost,
                    url: method,
                    contentType: 'application/json; charset=utf-8',
                    dataType: datatype,
                    cache: false,
                    async: false,
                    data: params,
                    success: function (dat) {
                        data = dat.d;

for // здесь все нормально работает
                    },
                    error: function (xhr, ajaxOptions, thrownError) {
                        ShowError(thrownError);
                    }
                });