Five steps to AJAX application

1. Create an xmlHttpRequest object

    if(window.XMLHttpRequest) {
    xmlHttp = new XMLHttpRequest();
    if(xmlHttp.overrideMimeType) {
     xmlHttp.overrideMimeType("text/xml");
    }
   } else if(window.ActiveXobject) {
    var activeName = ["MSXML2.XMLHTTP", "Microsoft.XMLHTTP"];
    for(var i = 0; i < activeName.length; i++) {
     try {
      xmlHttp = new ActiveXobject(activeName[i]);
      break;
     } catch(e) {}
    }
   }
   if(!xmlHttp) {
    alert("创建xmlhttprequest对象失败");
   } else {}

2. Set the callback function

   xmlHttp.onreadystatechange= callback;

   function callback(){}

3. Use the OPEN method to establish a connection with the server xmlHttp.open("get","ajax?name="+ name,true)

   In this step, pay attention to setting the http request method (post/get), if it is POST method, pay attention to setting the request header information xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded")

4. Send data to the server

  xmlHttp.send(null);

  If it is a POST method, it is not empty

5. Process for different response states in the callback function

  if(xmlHttp.readyState == 4){ //Determine whether the interaction is successful

      if(xmlHttp.status == 200){ //Get the data returned by the server //Get plain text data

        var responseText =xmlHttp.responseText;

       document.getElementById("info").innerHTML = responseText;

      }

   }