function checkEmail() {
var email = document.getElementById('emailaddress');
var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
if (!filter.test(email.value)) {
alert('Please provide a valid email address');
email.focus
return false;
}
document.getElementByName('email').value = '';
}