The regular expression for email validation is follows :

^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})$

The JS script for email validation can be written as follows :

function email_validator(mail_id) {
    var regexp=/^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})$/;
    if (regexp.test(mail_id)) {
        alert("This is a valid Email Id!!!");
        return true;
    }
    else {
        alert("This is an invalid Email Id!!!");
        return false;
    }
}