Make a div visible from an outside php - php

Question

I'm working on a log in session, and I want to display errors on the same page, for example - "Invalid Password" or "User does not exist".
Heres my code:
<?php
session_start();
mysql_connect('mysql.database.com','user','database')or die ('Connection Failed: '.mysql_error());
mysql_select_db('database')or die ('Error when selecting Database: '.mysql_error());
function remove($mensaje)
{
$nopermitidos = array("'",'\\','<','>',"\"");
$mensaje = str_replace($nopermitidos, "", $mensaje);
return $mensaje;
}
if(trim($_POST["usuario"]) != "" && trim($_POST["password"]) != "")
{
$usuario = strtolower(htmlentities($_POST["usuario"], ENT_QUOTES));
$password = $_POST["password"];
$result = mysql_query('SELECT password, usuario FROM usuarios WHERE usuario=\''.$usuario.'\'');
if($row = mysql_fetch_array($result)){
if($row["password"] == $password){
$_SESSION["k_username"] = $row['usuario'];
header( 'Location: diseno.php' ) ;
}else{
echo '<p class="message2">Invalid password</p>';
}
}else{
echo '<p class="message2"User does not exist</p>';
}
mysql_free_result($result);
}else{
echo '<p class="message2">Must enter a user and password</p>';
}
mysql_close();
?>
<SCRIPT LANGUAGE="javascript">
location.href = "index.php";
</SCRIPT>
As you can see that's my validation and action for the log in form. Instead of echoing errors in a new page I want to display it in the same page. I tried with javascript and it didn't work I used.
var page = document.URL = "http://www.mysite.com/login.php"
page.getElementById( 'wrongpassword' ).style.display = 'block';
All divs I want to display are set as none in the login.php file.
Anyone could help me?

Answer 1

The easiest way to accomplish this is to process the login and then include the PHP code which displays the normal page. I'm not sure how you've designed your site, but including index.php at the end might do the trick. Right now, you are using a JS redirect, which won't give you the result that you want.
Instead of echoing the message, I like to set a $message variable which includes the message. When you render the main page, simply echo this variable in the appropriate place if it is set.

Answer 2

For doing it simply you can make use of JQuery. I have done it on my website so I can say it really works.
Start your session, checking the values and either assign the value in global variables of javascript or print it there only
eg.
<?php
session_start();
//checking ur values
echo "<script src=\"js/jquery-1.8.3.min.js\"></script>
<script type=\"text/javascript\">
$(document).ready(function(){
//you can assign values here or print error messages to any div
('.div_class').html("unuthorised user");
});
</script>";
?>
Here I have used a downloaded JQuery file from
http://jquery.com/download/
You can choose other wise to use the online version of this JQuery file. The syntax for that is
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
Feel free to get back in case of any further query/issues regarding the above code.