function popup()
{
	window.open('popup.html','jevensternaam', 'width=300,height=400,scrollbars=no,toolbar=no,location=yes, menubar=no, directories=no,location=no, status=no');
}

function checkRequiredFields(input)
{

    var requiredFields = new Array("naam",
                                   "telefoon",
                                   "opm",
                                   "email");

    var fieldNames = new Array("Uw naam",
                               "Uw telefoonnummer",
                               "Uw vraag/commentaar",
                               "Uw e-mailadres");
    var fieldCheck   = true;
    var fieldsNeeded = "\nDe volgende velden zijn verplicht:\n\n\t";

    for(var fieldNum=0; fieldNum < requiredFields.length; fieldNum++) {
        if ((input.elements[requiredFields[fieldNum]].value == "") ||
            (input.elements[requiredFields[fieldNum]].value == " ")) {

            fieldsNeeded += fieldNames[fieldNum] + "\n\t";
            fieldCheck = false;
        }
    }

    if (fieldCheck == true)
    {
        return true;
    }
    else
    {
        alert(fieldsNeeded);
        return false;
    }
}