function GetAnnuityValue() {
  var url="03_getAnnuityValue.php";
  var payment=document.getElementById("payment").value;
  var interest=document.getElementById("interest").value;
  var years=document.getElementById("years").value;
  request.open("POST", url, true);
  request.onreadystatechange = updateInvestmentReturn;
  var postData = "payment=" + escape(payment) + "&interest=" + escape(interest) + "&years=" + escape(years);
  request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  request.send(postData);
}

function updateInvestmentReturn() {
  if (4 == request.readyState) {  // Connection to the server has finished
    if (200 == request.status) {  // We have a return status that means the server completed successfully
      var xmlDoc = request.responseXML;
      var xmlappError = xmlDoc.getElementsByTagName("app-error")[0];
      var errorEL = document.getElementById("appError");
      var investedEL = document.getElementById("invested");
      var fvaEL = document.getElementById("fva");
      if (xmlappError != null) {
        var appError = xmlappError.firstChild.nodeValue;
        replaceText(errorEL, appError);
        replaceText(investedEL, '$0');
        replaceText(fvaEL, '$0');
        return;
      }
      var xmlinvested = xmlDoc.getElementsByTagName("invested")[0];
      var invested = xmlinvested.firstChild.nodeValue;
      var xmlfva = xmlDoc.getElementsByTagName("fva")[0];
      var fva = xmlfva.firstChild.nodeValue;
      replaceText(investedEL, invested);
      replaceText(fvaEL, fva);
      replaceText(errorEL, '');
    } else {
      alert("Error! Request status is " + request.status);
      var message = request.getResponseHeader("Status");
      if ((null == message.length) || (message.length <= 0)) {
      } else {
        alert(message);
      }
    }
  }
}