<?php
/**
 * Redirect "Join Group" Button After Click.
 */
function yzc_redirect_join_group_button_to_group() {
    ?>
    <script type="text/javascript">
        jQuery( document ).ready( function(){

            $( '.join-group' ).on( 'click', function( e ) {

                e.stopImmediatePropagation();

                // Redirect to link
                window.location.href = $( this ).attr( 'href' );
            });
        });

    </script>
    <?php
}

add_action( 'wp_footer', 'yzc_redirect_join_group_button_to_group' );