Running Javascript function after variables are set

I have the following functions:

// NATION
var x, y, z;
function flag(nation,area)
{
x = nation;
this.nation=nation;
var el=document.getElementById("desc");
el.innerHTML='The region you have selected is <b>'+area+'</b>';
document.getElementById("flag").innerHTML='<img src="images/flags/'+nation+'.jpg">';
}
// SERVICE
function output(service)
{
y = service;
this.service=service;
var el=document.getElementById("service-desc");
el.innerHTML='You have selected a <b>'+service+'<开发者_高级运维;/b> service.';
document.getElementById("clock").innerHTML='<img src="images/clock-'+service+'.png">';
}

And once the user has set the variables: nation & service have been set then I would like to run this function:

function selectmodel()
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
  {
  alert ("Your browser does not support XMLHTTP!");
  return;
  }
var location=x;
var time=y;
var weight=z;
var url="selectmodel.php";
url=url+'?location='+location+'&time='+time+'&weight='+weight;
xmlhttp.onreadystatechange=stateChanged1;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
window.location.hash="slider";
}
function stateChanged1()
{
if (xmlhttp.readyState==4)
  {
  document.getElementById("result").innerHTML=xmlhttp.responseText;
  }
}

Please can somebody be knid enough to let me know how to do this?

Thanks, B.

EDIT - Sorry forgot to say that the variables are come from onclick's (onClick="flag('scotislands', 'Scottish islands');")

I guess you are looking - in true Javascript spirit - for some kind of event which is triggered, and perhaps there's even a way, but in this case I'd just call a check from each function:

var x = null;
var y = null;
var ...

function trySelectModel() {
  if (x == null) || (y == null) return;
  selectModel(); // Your function
}

function flag(...) {
  // Your existing code
  trySelectModel();
}

function output(service) {
  // Your existing code
  trySelectModel();
}

function selectmodel() {
  // Your existing code
}