function checkSubmit(f) {
    for (i=0; i<document.forms[f].elements.length; i++) {
        v = document.forms[f].elements[i].value;
        t = document.forms[f].elements[i].type;
        n = document.forms[f].elements[i].name;
        if (t=='text' || t == 'textarea' || t == 'file') {
            if (v == '' && n.substr(0,6) != 'extra_') {
                alert('Some mandatory fields are empty !');
                return false;
            }
        }
    }
    return true;
}