Redirect based on log-in status per JavaScript

To test if a user is logged in use is_user_logged_in().

To redirect a visitor use wp_redirect($location, $status = 302).

You can combine both:

<?php

$location = 'http://localhost';

if ( is_user_logged_in() )
    $location = admin_url( "https://wordpress.stackexchange.com/" );

wp_redirect( $location );

In JavaScript (sort of):

add_action( 'wp_footer', 'wpse_73701_button' );

function wpse_73701_button()
{
    $location = is_user_logged_in() ? admin_url( "https://wordpress.stackexchange.com/" ) : 'http://localhost';

    print "<button onclick='window.location.href=\"$location\"'>Click!</button>";
}

You could also just create JavaScript variables and use them in your scripts:

<script>
var isLoggedIn = <?php print is_user_logged_in() ? 'true' : 'false'; ?>;
var redirectTo = '<?php print is_user_logged_in() ? admin_url( "https://wordpress.stackexchange.com/" ) : 'http://localhost'; ?>';
</script>