JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.js"></script>
<form id="signupform">
<input id="username" name="username" />
    <br/ >
<input id="email" name="email" />
    <br />
<input id="submit" type="submit" value="submit" />   
</form>

JavaScript

$.validator.addMethod("user_email_not_same", function(value, element) {
   return $('#username').val() != $('#email').val()
}, "* User and Email should not match");

// validate form    
$("#signupform").validate({

    rules: {
        username: {
            required: true,
            user_email_not_same: true
        },
        email: {
            required: true,
            user_email_not_same: true
        },
    },
});