Check if on Custom Post Type for TinyMCE buttons

I’m adding TinyMCE buttons to my plugin and they’re working, but I only want these buttons to show up for a certain custom post type. I followed this tutorial if it helps:

WordPress Shortcode TinyMCE Button Tutorial Part 2

How can I have that check if they are editing/posting a post in a custom post type of lets say, newpages?

If you followed that tutorial you linked then look at the function that registers the buttons:

function mylink_button() {
   if ( ! current_user_can('edit_posts') && ! current_user_can('edit_pages'){
     return;
   }
   if ( get_user_option('rich_editing') == 'true' ) {
     add_filter( 'mce_external_plugins', 'add_plugin' );
     add_filter( 'mce_buttons', 'register_button' );
   }
}

and you change it a bit to check for the post type:

function mylink_button() {
        if ( ! current_user_can('edit_posts') && ! current_user_can('edit_pages')){
         return;
        }
        if ( get_user_option('rich_editing') == 'true' ) {
            global $typenow;
            if (empty($typenow) && !empty($_GET['post'])) {
                $post = get_post($_GET['post']);
                $typenow = $post->post_type;
            }
            if ("newpages" == $typenow){
                add_filter( 'mce_external_plugins', 'add_plugin' );
                add_filter( 'mce_buttons', 'register_button' );
            }
       }
    }

this way you only register the buttons on your “newpages” type