JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.18/themes/flick/jquery-ui.css">

<input type="text" id="txtEmail"/>

<br />

<input type="button" id="btnValidate" value="click me to validate" />

JavaScript

function validateEmail(sEmail) {
    var filter = /^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
    if (filter.test(sEmail)) {
        return true;
    }
    else {
        return false;
    }
}

$(document).ready(function() {
   $('#btnValidate').click(function() {
        var sEmail = $('#txtEmail').val();
        if ($.trim(sEmail).length == 0) {
            alert('Please enter valid email address');
            e.preventDefault();
        }
        if (validateEmail(sEmail)) {
            alert('Email is valid');
        }
        else {
            alert('Invalid Email Address');
            e.preventDefault();
        }
    });
});