Form Validation Tutorial Using Javascript, Php And Ajax!

<?php
session_start();

if(isset($_SESSION['login_user'])||$_SESSION['login_user']!="") {
header("Location:index2.php");
}


$username = $_REQUEST['username'];
$password = $_REQUEST['password'];

//let us assume the right username is 'dhtml' and password is 'jscript'
if($username!=""&&$password!="") {
//validate details
if($username=="dhtml"&&$password=="jscript") {
//correct login
$_SESSION['login_user']="$username";
header("Location:index2.php");
die(); //to prevent moving forward pending redirection
} else {
//in-correct login
$msg=<<<end
Your <b>username/password</b> is in-correct.
end;
}

}
?>

<title>My Secure Site</title>

<script>
function validate(form) {
with(form) {
if(username.value=="") {alert("Please enter your username to continue.");username.focus();return false;}
if(password.value=="") {alert("Please enter your password to continue.");password.focus();return false;}
}
return true;
}
</script>

<?php
if($msg!="") {
print<<<end
<font color="red">* </font>
<font color="blue">$msg</font>
<br><br>

end;
}
?>

<b>Please Login to continue.</b>

<table>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" onsubmit="return validate(this)">
<tr>
<td>Username:</td>
<td><input type="text" name="username" value="<?php echo $_REQUEST['username']; ?>"></td>
</tr>
<tr>
<td>Password:</td>
<td><input type="password" name="password"></td>
</tr>
<tr>
<td>&nbsp;</td>
<td align="center">
<input type="submit" value="Continue">
</td>
</tr>
</form>
</table>

<?php session_start();
if(!isset($_SESSION['login_user'])||$_SESSION['login_user']=="") {
header("Location:index.php");
}
?>

<title>Personalized Home Page</title>

Welcome <?php echo $_SESSION['login_user'];?>, <a href="logout.php">Logout</a>
<br><br>
if you can see this page, then that would mean that you are correctly logged in.

<?php
session_start();

if(isset($_SESSION['login_user'])||$_SESSION['login_user']!="") {
header("Location:index2.php");
}
?>

<title>My Secure Site</title>

<script>
function ajaxRequest(){
var activexmodes=["Msxml2.XMLHTTP", "Microsoft.XMLHTTP"] //activeX versions to check for in IE
if (window.ActiveXObject){ //Test for support for ActiveXObject in IE first (as XMLHttpRequest in IE7 is broken)
  for (var i=0; i<activexmodes.length; i++){
   try{
    return new ActiveXObject(activexmodes[i])
   }
   catch(e){
    //suppress error
   }
  }
}
else if (window.XMLHttpRequest) // if Mozilla, Safari etc
  return new XMLHttpRequest()
else
  return false
}


function validate(form) {
with(form) {
if(username.value=="") {alert("Please enter your username to continue.");username.focus();return false;}
if(password.value=="") {alert("Please enter your password to continue.");password.focus();return false;}
}


var mygetrequest=new ajaxRequest()
mygetrequest.onreadystatechange=function(){
if (mygetrequest.readyState==4){
  if (mygetrequest.status==200 || window.location.href.indexOf("http")==-1){
   var res=mygetrequest.responseText
   if(res=="ok") {location.href="index2.php";} else {alert(res);}
  }
  else{
   alert("An error has occured making the request")
  }
}
}

var username_val=encodeURIComponent(form.username.value)
var password_val=encodeURIComponent(form.password.value)
var link="login.php?username="+username_val+"&password="+password_val;
mygetrequest.open("GET",link, true)
mygetrequest.send(null)

return false;
}
</script>

<?php
if($msg!="") {
print<<<end
<font color="red">* </font>
<font color="blue">$msg</font>
<br><br>

end;
}
?>

<b>Please Login to continue.</b>

<table>
<form action="login.php" onsubmit="return validate(this)">
<tr>
<td>Username:</td>
<td><input type="text" name="username" value="<?php echo $_REQUEST['username']; ?>"></td>
</tr>
<tr>
<td>Password:</td>
<td><input type="password" name="password"></td>
</tr>
<tr>
<td>&nbsp;</td>
<td align="center">
<input type="submit" value="Continue">
</td>
</tr>
</form>
</table>