function testInput()
{
    if(this.document.getElementById("voornaam").value == "" || 
       this.document.getElementById("achternaam").value == "" ||
       this.document.getElementById("adres").value == "" ||
       this.document.getElementById("postcode").value == "" ||
       this.document.getElementById("woonplaats").value == "" ||
       this.document.getElementById("email").value == "" ||
       this.document.getElementById("vraag").value == "")
    {
        alert("Niet alles is ingevuld.");
    }
    else
    {
        document.naw_form.submit();
    }
}