I can't figure out why my global variable workRegionCode is not set properly.

In function getWorkRegion(), after getting ajax callback, it attempt to set workRegionCode global variable. (inside of function setFirstIndexWorkRegionCode() ).

The alert in setFirstIndexWorkRegionCode() outputs expected value like 401 or 123 etc.

But then when getMachines() is called, the global variable workRegionCode is undefiend :(

This js starts from window.onload()

(please ignore those Japanese JSON key value and few Japanese variables. They are harmless)

Code:

    var workRegionDropdown = document.getElementById("workRegionDropdown");;
    var machineDropdown = document.getElementById("machineDropdown");

    //this is the global variable with problem.....
    var workRegionCode;

    //INIT
    window.onload = function() {

        getWorkRegions();

       // alert("before: " + window.workRegionCode);

        getMachines();

      //  alert("after: " + window.workRegionCode);
    }

    function addWorkRegionToDropdown(jsonObject, dropdown) {
        for(var i=0, j=jsonObject.length; i<j; i++) {
            var option = document.createElement("option");
            option.text = jsonObject[i].?????? + ":" + jsonObject[i].??????;
            option.value = jsonObject[i].??????;
            dropdown.options.add(option);
        }
    }

    function addMachineToDropdown(jsonObject, dropdown) {
        for(var i=0, j=jsonObject.length; i<j; i++) {
            var option = document.createElement("option");
            option.text = jsonObject[i].???;
            option.value = jsonObject[i].???;
            dropdown.options.add(option);
        }
    }


    function getMachines() {

        //!!!!!!!!!!! workRegionCode is undefined.. why?!?!?!  

        alert("inside of getMachines() ==> " + window.workRegionCode);

        var ajaxRequest = new XMLHttpRequest();
        ajaxTimeout = setTimeout(function() {timeoutAjax(ajaxRequest, "showMessage")}, "5000");

        ajaxRequest.onreadystatechange = function() {
            if(ajaxRequest.readyState == 4  ) {
                clearTimeout(ajaxTimeout);
                switch ( ajaxRequest.status ) {
                    case  200:
                                var jsonOut = JSON.parse(ajaxRequest.responseText);
                                addMachineToDropdown(jsonOut.??, machineDropdown);
                                break;
                    default:

                                document.getElementById("showMessage").innerHTML = ajaxRequest.responseText;
                }
            }
        }


        var aMonthAgo = new Date();
        with(aMonthAgo) {
            setMonth(getMonth() - 1)
        }
        aMonthAgo = aMonthAgo.getYYYYMMDD();
        var ??? = "29991231";

        var url = "../resources/machine/list/" + window.workRegionCode + "/" + aMonthAgo + "/" + ???;
        ajaxRequest.open("GET", url, true);
        ajaxRequest.send(null)
    }




    function getWorkRegions() {
        var ajaxRequest = new XMLHttpRequest();
        ajaxTimeout = setTimeout(function() {timeoutAjax(ajaxRequest, "showMessage")}, "5000");

        ajaxRequest.onreadystatechange = function() {
            if(ajaxRequest.readyState == 4  ) {
                clearTimeout(ajaxTimeout);
                switch ( ajaxRequest.status ) {
                    case  200:
                                var jsonOut = JSON.parse(ajaxRequest.responseText);

                                //set global variable workRegionCode
                                setFirstIndexWorkRegionCode(jsonOut);

                                addWorkRegionToDropdown(jsonOut.???, workRegionDropdown);
                    default:

                                document.getElementById("showMessage").innerHTML = ajaxRequest.responseText;
                }
            }
        }

        var url = "../resources/workshop/list";
        ajaxRequest.open("GET", url, true);
        ajaxRequest.send(null)
    }//end getWorkRegions()

    function setFirstIndexWorkRegionCode(jsonString) {

        //here I set the value to work region code!
        window.workRegionCode = jsonString.???[0].??????;
        alert("??????: " + window.workRegionCode);

     }