var xmlHttp = null;

function GetCustomerInfo() {
  var CustomerNumber = document.getElementById("TextBoxCustomerNumber").value;
  var Url = "GetCustomerInfoAsJson.aspx?number=" + CustomerNumber;

  xmlHttp = new XMLHttpRequest();
  xmlHttp.onreadystatechange = ProcessRequest;
  xmlHttp.open("GET", Url, true);
  xmlHttp.send(null);
}

function ProcessRequest() {
  if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
    if (xmlHttp.responseText == "Not found") {
      document.getElementById("TextBoxCustomerName").value = "Not found";
      document.getElementById("TextBoxCustomerAddress").value = "";
    } else {
      var info = eval("(" + xmlHttp.responseText + ")");

      // No parsing necessary with JSON!        
      document.getElementById("TextBoxCustomerName").value = info.jsonData[0].cmname;
      document.getElementById("TextBoxCustomerAddress").value = info.jsonData[0].cmaddr1;
    }
  }
}