A case study of native Ajax notation _ajax related

In this paper, we analyze the native Ajax notation. Share to everyone for your reference. The specific analysis is as follows:

Although many JS frameworks now provide Ajax call methods, we do not even have to understand their specific implementation of the principle can be directly invoked, but I do not think from the most basic level to understand a thing, it is difficult to do the best.

var xhr=null; 
if (window. XMLHttpRequest) { 
  //non ie kernel 
  XHR = new XMLHttpRequest (); 
} else if (window. ActiveXObject) { 
  //IE kernel, where earlier versions of IE are written differently, can be queried under 
  XHR = new ActiveXObject ("Microsoft.XMLHTTP"); 
} else { 
  XHR = null; 
} 
 
if (XHR) { 
  xhr.open ("Get", "ajaxserver.action"); 
 
  Xhr.onreadystatechange = function () { 
    ///readystate Value Description 
    //0, initialization, XHR object already created, open 
    //1 not executed, loading, already called Open method , but did not send the request 
    //2, loading completed, request has been sent to complete 
    //3, interactive, can receive some 
 
    data/Status Value Description 
    //200: Success 
    //404: No files, queries or URLs found 
    //500: Server generates internal error 
    if (xhr.readystate = = 4 && Xhr.status = =) {// 
      here can handle the returned content 
      ///generally return JS On or XML data format 
      Console.log (xhr.responsetext); 
      Active release, JS itself will also be recycled 
      XHR = null; 
    } 
  ; 
  Xhr.send (); 
}

I hope this article will help you with your AJAX programming.