Change button text with user name using jQuery after user login

Use this code bellow:

<?php if ( is_user_logged_in() ) : ?>

    <li> <a href="https://wordpress.stackexchange.com/questions/269073/<?php echo wp_logout_url( get_permalink() ); ?>">Logout</a></li>

<?php else : ?>

    <li> <a href="http://your-site-name/login/">Login</a></li>

<?php endif;?>

UPDATE

       <?php if ( is_user_logged_in() ) :
$current_user = wp_get_current_user();
 ?>

            <li> <a href="https://wordpress.stackexchange.com/questions/269073/<?php echo wp_logout_url( get_permalink() ); ?>">Logout</a></li>
    <li>Username:  <?php echo $current_user->user_login; ?></li>
        <?php else : ?>

            <li> <a href="http://your-site-name/login/">Login</a></li>

        <?php endif;?>