function verplicht(field,alerttxt)
{
with (field)
{
if (value==null||value=="")
  {alert(alerttxt);return false}
else {return true}
}
}
function valideer(thisform)
{
with (thisform)
{
if (verplicht(afzender,"Fill out your name!")==false)
  {afzender.focus();return false}
else if (verplicht(email,"Fill out your email address!")==false)
  {email.focus();return false}
else if (verplicht(reactie,"Fill out a message!")==false)
  {reactie.focus();return false}
}
}