Anonymous

<script type="text/javascript">				function get(id) {		return document.getElementById(id);	}				function ajax() {		var xmlHttp;		try {			xmlHttp=new XMLHttpRequest(); 		}		catch (e) {			try	{				xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");			}			catch (e) {				try {					xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");				}				catch (e) {					return false;				}			}		}		return xmlHttp;	}		ajax = ajax();		function checkUsername() {				ajax.onreadystatechange = function() {			if(ajax.readyState == 4) {				get('ajax_output_node').innerHTML = ajax.responseText;			}		}		ajax.open("POST","ajax/register_ajax.php",true);		ajax.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');		ajax.send('username=' + get('id_username').value);	}		</script>used in:<input onkeyup="checkUsername();" type="text" name="username" id="id_username" value="<?php if (isset($_POST['username'])) { echo $_POST['username']; }?>" />