<script language="JavaScript1.2" type="text/javascript">
function makeRequest(url) {
	var httpRequest;
 
    if (window.XMLHttpRequest) { // Mozilla, Safari, ...
    	httpRequest = new XMLHttpRequest();
        if (httpRequest.overrideMimeType) {
        	httpRequest.overrideMimeType('text/xml');
        }
    } 
    else if (window.ActiveXObject) { // IE
    	try {
        	httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } 
        catch (e) {
        	try {
            	httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } 
            catch (e) {}
        }
	}
 
    if (!httpRequest) {
    	alert('Giving up :( Cannot create an XMLHTTP instance');
        return false;
    }
 
    httpRequest.onreadystatechange = function() { alertContents(httpRequest); };
    httpRequest.open('GET', url, true);
    httpRequest.send('');
 
}
 
// Function to deal with returned request
function alertContents(httpRequest) {
	if (httpRequest.readyState == 4) {
    	if (httpRequest.status == 200) {
			changeText(httpRequest.responseText);
			//alert(httpRequest.responseText);
        } else {
            alert('There was a problem with the request. '+httpRequest.status);
        }        
	}
}
 
Then with is in the page you only have to make your own function in JS to deal with the reply back from your script on the webserver. 
 
function changeText(){
    // This is were you put your script to handel if it is the same or not. 
}
</script>