Analysis of AJAX usage examples in javascript_javascript skills

var xhr = null; 
if(window.XMLHttpRequest){ //非IE浏览器 
  xhr = window.XMLHttpRequest; 
}else if(window.ActiveXObject){ //IE浏览器 
  try{   //高版本，受msxml3.dll+支持 
    xhr = new ActiveXObject("Msxml2.XMLHTTP"); 
  }catch(e){ 
    try{  // 低版本，msxml2.6以下版本使用 
     xhr = new ActiveXObject("Microsoft.XMLHTTP"); 
    }catch(e){ 
     alert("IE浏览器无法创建ActiveXObject对象！"); 
    } 
  } 
}

xhr.open("POST",url,true); 
xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
xhr.onreadystatechange=stateChangeHandler; 
xhr.send(); //var name="clf"; xhr.send(name); 
function stateChangeHandler(){ 
  if(xhr.readystate==4&&xhr.status==200){ 
   var obj = document.getElementById("targetDiv"); 
  obj.innerHTML = xhr.responseText; 
  } 
}