简单示例：AJAX结合PHP代码实现登录

                页面1: login.html
               
               
                html>
head>
script language="javascript">
function postRequest(strURL){
    var xmlHttp;
    if(window.XMLHttpRequest){ // For Mozilla, Safari, ...
        var xmlHttp = new XMLHttpRequest();
    }
    else if(window.ActiveXObject){ // For Internet Explorer
        var xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlHttp.open('POST', strURL, true);
    xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xmlHttp.onreadystatechange = function(){
        if (xmlHttp.readyState == 4){
            updatepage(xmlHttp.responseText);
        }
    }
    xmlHttp.send(strURL);
}
function updatepage(str){
    if(str=="yes"){
        alert("Welcome User");
    }else{
        alert("Invalid Login! Please try again!");
    }
}
function call_login(){
    var username = window.document.f1.username.value;
    var password = window.document.f1.password.value;
    var url = "login.php?username=" + username + "&password=" +password ;
    postRequest(url);
}
/script>
/head>
body>
Center>
form name="f1" onSubmit="return call_login();">
table border="0" bgcolor="#CCCCCC" cellspacing="1" cellpadding="3" width="316">
    tr>
        td align="left" colspan="2">b>font size="5" color="#000080">Login/font>/b>/td>
    /tr>
    tr>
        td align="right" width="124">b>font color="#000080">User Name:/font>/b>/td>
        td width="177">input type="text" name="username" id="user" size="20" value="" />/td>
    /tr>
    tr>
        td align="right" width="124">b>font color="#000080">Password:/font>/b>/td>
        td width="177">input type="password" name="password" size="20" value="" />/td>
    /tr>
    tr>
        td colspan="2" align="center">input type="button" name="a1" value="Login" onClick="call_login()">/td>
    /tr>
/table>
/form>
/center>
/body>
/html>
页面2: login.php
?
$username=$_GET["username"];
$password=$_GET["password"];
if($username=="admin" && $password=="admin"){
    echo "yes";
}else{
    echo "No";
}
?>