function checkSubmit() {

var companyName = document.getElementById('companyName').value;

var contactPerson = document.getElementById('contactPerson').value;

var email = document.getElementById('email').value;

var telNumber = document.getElementById('telNumber').value;



if (companyName == '' || companyName == 'bedrijfsnaam *') {

alert('U dient uw bedrijfsnaam in te vullen!');

return false;    

}



if (contactPerson == '' || contactPerson == 'contactpersoon *') {

alert('U dient uw contactpersoon in te vullen!');

return false;    

}



if (!email.match(/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i)) {

alert('Ongeldig e-mailadres!');

return false;                                    

}    



if (telNumber == '' || telNumber == 'telefoon *') {

alert('U dient uw telefoonnummer in te vullen!');

return false;    

}



}