[jQuery] Way of code execution?

[r1u0...@gmail.com]

Hi,
I've got following code:

 var tr;
                function updateNummbers(typ) {
                    var ret = "";

                    $.ajax({ type: "POST",
                        url: "DFWebService.asmx/getNummbers",
                        dataType: "text",
                        data: "typ=" + typ,
                        processData: false,
                        error: function(XMLHttpRequest, textStatus,
errorThrown) { ajaxError(XMLHttpRequest, textStatus, errorThrown); },
                        success: function(xml) {
                            ret = $(xml.replace(/&lt;/g, "<").replace(/&gt;/
g, ">")).find('anzahl').text();
                            tr = ret;
                            alert(tr); // OK
                            alert(ret); // OK
                        }
                    });
                alert(ret);      // VALUE ""
                }
                updateNummbers('new');
               alert(tr); // NO VALUE


it is placed in

        $(document).ready(
            function() {

I don't know why the value of updated variable tr outside function
updateNummbers don't exists. In alert inside this function value is
ok, but then I put alert after the function values are not correct.
The same situation is for variable ret.

Can anyone explain that to me?