Ajax make Form Validation sample

Ajax functions are mainly used in JS, Ajax does not require ASP, ASP is responsible for the background display and operation of the server data.
You can think like this:
1. Write form the first item (such as user name)
2.onblur event (lost focus) begins validation when it occurs, onblur= "Checkusername ()"
3.js send a request to the first ASP (assuming ajaxusername.asp) if the user is found from the database, give 1 (ajaxusername.asp all content is a 1) as
<%
if (User.exist ()) Response.Write "1"
%>
4.js received, the checkuser () function is automatically executed.
CheckUser the user name line background color change, and show "the user has already existed"

You wrote the ASP section yourself. Some JS code is given below.
<script>
/* The following functions generally do not need to change * *
var Ajax;
function Createajax () {
if (window. XMLHttpRequest) {
Ajax = new XMLHttpRequest ();
}else if (window. ActiveXObject) {
Ajax = new ActiveXObject ("Microsoft.XMLHTTP");
}
}
function SendData (url_,sendtext_) {
Ajax.open ("POST", url_,true);
Ajax.onreadystatechange = checkuser;
Ajax.send (Sendtext_);
}
function Checkajaxstatus (ajax_) {
if (ajax_.readystate = 4)
if (Ajax_.status = 200)
return true;
return false;
}
/* The above function generally does not need to change * *
function checkuser () {
if (! Checkajaxstatus (Ajax)) return;
The ASP returns the processing of the result to the fruit. The server returns the ajaxusername.asp, which is stored in the Ajax.responsetext property.

}

function Checkusername () {
Createajax ();
SendData ("ajaxusername.jsp", "username=" + name);
}

</script>