function validateaantal(e){
    var keynum;
    var keychar;
    var numcheck;

    if(window.event) // IE
    {
        keynum = e.keyCode;
    }
    else if(e.which) // Netscape/Firefox/Opera
    {
        keynum = e.which;
    }

    keychar = String.fromCharCode(keynum);

    numcheck = /\d/;

    return numcheck.test(keychar)
}

function change(ref){
    window.location.replace("execute.php?page=changeaantal&ref=" + ref + "&aantal=" + document.getElementById('aantal' + ref).value);
}