sprawdzanie czy jest dana nazwa uzytkownika wolna Ajax

user_check.php

$('#username').change(function(){} - username is the ID of the input. Using $("#username").val("id") calling input field value. First checking the value string length max 3 (username.length > 3)) 

check_ajax.php
Contains PHP code.

 
'.$username.' is already in use.';
 }
else
 {
echo 'OK';
 }
 }
?>

CSS Code

body
 {
 font-family:Arial, Helvetica, sans-serif
 }
#status
 {
 font-size:11px;
 margin-left:10px;
 }
.green
 {
 background-color:#CEFFCE;
 }
.red
 {
 background-color:#FFD9D9;
 }