// JavaScript Document
var objRequest = createRequestObject();

    function createRequestObject() {
      var objTemp = false;

      if (window.XMLHttpRequest) {
        objTemp = new XMLHttpRequest();
      }
      else if (window.ActiveXObject) {
        objTemp = new ActiveXObject("Microsoft.XMLHTTP");
      }
      return objTemp;
    }

function getData(dataSource){
      if(objRequest) {
         objRequest.open("GET",dataSource);
         objRequest.onreadystatechange = handleResponse;
         objRequest.send(null);
      }
   }
   
function checkUsername(keyEvent){
   var userName = document.getElementById("username");
      keyEvent = (keyEvent) ? keyEvent : window.event;
      
      if(keyEvent.type == "click"){
         if(userName.value){
                  getData("check_username.php?name="+encodeURIComponent(userName.value));
               }
         }   }   
   
function handleResponse(){
      if(objRequest.readyState == 4 && objRequest.status == 200){
            var status = objRequest.responseText;
            alert(status);
            if(status == "ok"){
                  alert("username is valid!!");
                  
               }else if(status == "used"){
                  alert("This username is no longer available");
                  }
         }
      
   }