JS implementation Ajax Request __JS

Using XMLHttpRequest to send AJAX requests
1. Create an object:
function Createxmlhttp () {
var xmlHttp;
try{
xmlhttp= new XMLHttpRequest ();
}catch (e) {
try{
Ie
xmlhttp= new ActiveXObject ("Msxml2.xmlhttp");
}catch (e) {
try{
Ie
xmlhttp= new ActiveXObject ("Microsoft.XMLHTTP");
}catch (e) {

}
}
}
}
2, registration monitoring, that is, callback function.
var data = null;
var xmlHttp = Createxmlhttp ();
Xmlhttp.onreadystatechange=function () {
if (xmlhttp.readystate==4) {
if (xmlhttp.status==200| | xmlhttp.status==304) {
data = Xmlhttp.responsetext;
}
}
}
3, open the connection
Xmlhttp.open ("Get", "Getdata.servlet", true);
The third parameter represents an asynchronous request
4, send the request
Set Request headers
Xmlhttp.setrequestheader ("Content-type", "application/x-www-form-urlencoded");
Get mode
Xmlhttp.send (NULL);
Post method
Xmlhttp.send ("a=1&b=2");