JSFiddle - React, Tailwind, and code Playground

HTML

<form id="fbsignup">
    <input type="text" class="firstname" />
    <input type="text" class="lastname" />
    <input type="text" class="email" />
</form>

CSS

.error { color: #ff0000; }

JavaScript

$(document).ready(
    function()
    {
        var failedElements = $("#fbsignup input").filter(".firstname[value=''], .lastname[value=''], .email[value='']");
        
        if (failedElements.length > 0)
        {
            failedElements.after("<span class='error'>*</span>");            
            return false;
        }
        
        return true
    });