function changeText() {
    document.getElementById('linkoptredens').innerHTML = 'Terug';
    document.getElementById('linkoptredens').setAttribute("onclick", "changeTextBack()");
    document.getElementById('linkoptredens').href = 'events/eventspast.php'
}
function changeTextBack() {
    document.getElementById('linkoptredens').innerHTML = 'Archief';
    document.getElementById('linkoptredens').setAttribute("onclick", "changeText()");
    document.getElementById('linkoptredens').href = 'events/events.php';
}