function getXMLHttp() {
    http_request = false;
    if (window.XMLHttpRequest) {
        http_request = new XMLHttpRequest();
        if (http_request.overrideMimeType) {
        }
    } else if (window.ActiveXObject) {
        try {
            http_request = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                http_request = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) { }
        }
    }
    if (!http_request) {
        alert('Giving up :( Cannot create an XMLHTTP instance');
        return false;
    }
    else {
        return http_request;
    }
}

function faiquellochedevifare() {
    document.getElementById('div1').innerHTML = '<img src="immagine_loading.gif" alt="loading" /> Caricamento in corso...';
    
    objHTTP = getXMLHttp()
    objHTTP.open("POST", "file_che_elaborerà_i_dati.aspx", "false");
    objHTTP.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    objHTTP.onreadystatechange = function() { fineelab(); }
    objHTTP.send('parametro1=0&parametro2=0');
}

function fineelab() {
   if (objHTTP.readyState == 4) {
        if (objHTTP.status == 200) {
            document.getElementById('div1').innerHTML = objHTTP.responseText;
        }
     }
}