var pop = null;

function popdown() {
    if (pop && !pop.closed) pop.close();
}

function popup(obj,w,h) {
    var url = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;

    if (!url) return true;

    var args = 'width='+w+',height='+h+',resizable';
    popdown();
    pop = window.open(url,'',args);
    return (pop) ? false : true;
}

window.onunload = popdown;
window.onfocus = popdown;