var xmlhttp;

function loadXMLDoc(url) {
    // IE7/8, FF, CHROME
    try {
        xmlhttp = new XMLHttpRequest();
    }
    catch (e) {
        throw new Error("This browser does not support XMLHttpRequest.")
    }

    xmlhttp.onreadystatechange = state_Change;
    xmlhttp.open("GET", url, true);
    xmlhttp.send(null);
}

//0 = uninitialized
//1 = loading
//2 = loaded
//3 = interactive
//4 = complete