function checkForm() {
if (document.forms.contactForm.elements['custName'].value.length == 0) {
    alert('Please enter a value for the "Your name" field');
    return false;
}
if (document.forms.contactForm.elements['custEmail'].value.length == 0) {
    alert('Please enter a value for the "Your email address" field');
    return false;
}
if (document.forms.contactForm.elements['custComment'].value.length == 0) {
    alert('Please enter a value for the "Comments" field');
    return false;
}
   return true;
}