var _activated_form = null;

function change_gallery(gallery_chooser) {
    var gallery_id = gallery_chooser.options[gallery_chooser.selectedIndex].value;
    location.href = '/gallery.php?gallery=' + gallery_id;
}

function change_page() {
    var gallery_id  = _activated_form.gallery_id.value;
    var page        = _activated_form.page.value;
    location.href 
        = '/gallery.php?gallery=' + gallery_id + '&page=' + page ;
}

function validate_new_page(form) {
    var gallery_id  = form.gallery_id.value;

    if (isNotEmpty(form.page)) {
        if (isInteger(form.page)) {
            if (isSmaller(form.page, form.max_page)) {
                if (isPositive(form.page)) {
                    _activated_form = form;
                    return true;
                }
            }
        }
    }
    _activated_form = null;
    return false;
}