JSFiddle - React, Tailwind, and code Playground

HTML

<form>
        Username<br />
        <input type="text" id="user_input" name="username" /><br />
        Password<br />
        <input type="text" id="pass_input" name="password" /><br />
        Confirm Password<br />
        <input type="text" id="v_pass_input" name="v_password" /><br />
        Email<br />
        <input type="text" id="email" name="email" /><br />     
        <input type="submit" id="register" value="Register" />
        </form>
        <div id="test">
        </div>

JavaScript

function buttonState(){
    $("input").each(function(){
        $('#register').attr('disabled', 'disabled');
        if($(this).val() == "" ) return false;
        $('#register').attr('disabled', '');
    })
}

$(function(){
    $('#register').attr('disabled', 'disabled');
    $('input').change(buttonState);
})