function dosubmit( ) {
       
    var elLength = document.compare.elements.length;
    var hasChecked = false;
    for (i=0; i<elLength; i++)
    {
        var type = document.compare.elements[i].type;
        if (type=="checkbox" && document.compare.elements[i].checked){            
            hasChecked = true;
        }
    }       
    if (!hasChecked){  
        alert('Selecteer alstublieft één of meerdere kredietkaarten.')
        return
      }    
    document.compare.submit();
}