Check email is valid

<script type="text/javascript">
function checkEmail() {
var email = document.getElementById('email');
var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
if (!filter.test(email.value)) {
alert('Hay nhap dia chi email hop le.\nExample@gmail.com');
email.focus;
return false;
}else{
alert('OK roi day, Email nay hop le.');
}
}</script>

(http://www.24kho.com/@forum/threads/4758-Check-Email-Validate-with-Javascript-and-Regular-Expressions-Kiem-tra-tinh-hop-le-cua-email)
Source: http://www.24kho.com/@forum/threads/4758-Check-Email-Validate-with-Javascript-and-Regular-Expressions-Kiem-tra-tinh-hop-le-cua-email#ixzz1aNpsM9Pl