function trim(str, chars) {
    return ltrim(rtrim(str, chars), chars);
}

function ltrim(str, chars) {
    chars = chars || "\\s";
    return str.replace(new RegExp("^[" + chars + "]+", "g"), "");
}

function rtrim(str, chars) {
    chars = chars || "\\s";
    return str.replace(new RegExp("[" + chars + "]+$", "g"), "");
}

function checkform ( form )
{
    var velden = "";
    var test = true;

    if (trim(form.naam.value) == "") {
        velden += "\r\n- " + document.getElementById("labelnaam").innerHTML;
        form.email.focus();
        test = false;
    }

    if (trim(form.straat.value) == "") {
        velden += "\r\n- " + document.getElementById("labelstraat").innerHTML;
        form.email.focus();
        test = false;
    }

    if (trim(form.stad.value) == "") {
        velden += "\r\n- " + document.getElementById("labelstad").innerHTML;
        form.email.focus();
        test = false;
    }

    if (trim(form.email.value) == "") {
        velden += "\r\n- " + document.getElementById("labelemail").innerHTML;
        form.email.focus();
        test = false;
    }
    
    myOption = -1;
    for (i=form.betalingswijze.length-1; i > -1; i--) {
        if (form.betalingswijze[i].checked) {
            myOption = i;
            i = -1;
        }
    }
    if (myOption == -1) {
        velden += "\r\n- " + document.getElementById("labelbetalingswijze").innerHTML;
        test = false;
    }

    if(!test)
    {
        alert(document.getElementById("errormessage").value + velden);
    }

    return test ;
}