function LivePageWidth() {
    if (window.innerWidth!= null)
        return window.innerWidth;
    if (document.body.clientWidth!= null)
        return document.body.clientWidth;
    return screen.availWidth;
}
function chageHead() {
    var objMiddle=document.getElementById('middle');
    if (!objMiddle) return false;
    var winWidth=LivePageWidth();
    if (winWidth>1247) {
        objMiddle.width=eval(winWidth-1245);
    } else {
        objMiddle.width=10;
    }
}

window.onresize=chageHead;
window.onload=chageHead;