how to add validations for email in nodejs code example

Example 1: how to validate email in node js

var emailRegex = /^[-!#$%&'*+\/0-9=?A-Z^_a-z{|}~](\.?[-!#$%&'*+\/0-9=?A-Z^_a-z`{|}~])*@[a-zA-Z0-9](-*\.?[a-zA-Z0-9])*\.[a-zA-Z](-?[a-zA-Z0-9])+$/;

function isEmailValid(email) {
    if (!email)
        return false;

    if(email.length>254)
        return false;

    var valid = emailRegex.test(email);
    if(!valid)
        return false;

    // Further checking of some things regex can't handle
    var parts = email.split("@");
    if(parts[0].length>64)
        return false;

    var domainParts = parts[1].split(".");
    if(domainParts.some(function(part) { return part.length>63; }))
        return false;

    return true;
}

Example 2: how to set validation for email in javascript

<script language="javascript">

function checkEmail() {

    var email = document.getElementById('txtEmail');
    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;
 }
}</script>