Add Button to TinyMCE Custom Menu

I've added a new button with a menu to the TinyMCE visual editor using this tremendously helpful tutorial but would now like to add further items to this menu depending on whether various post types are active in my theme. I think I'm on the right track with addMenuItem and 'context' but can't figure out how to set this up in the correct order.

My plugin code:

add_action('admin_head', 'nto_add_shortcode_button');

function nto_add_shortcode_button() {
    global $typenow;

    // check user permissions
    if ( !current_user_can('edit_posts')  !current_user_can('edit_pages') ) {
        return;
    }

    // verify the post type
    if( ! in_array( $typenow, array( 'post', 'page' ) ) )
        return;

    // check if WYSIWYG is enabled
    if ( get_user_option('rich_editing') == 'true') {
        add_filter("mce_external_plugins", "nto_add_tinymce_plugin");
        add_filter('mce_buttons', 'nto_register_my_tc_button');
    }
}

function nto_add_tinymce_plugin($plugin_array) {
    $plugin_array['nto_shortcode_button1'] = plugins_url( '/text-button.js', __FILE__ );
    return $plugin_array;
}

function nto_register_my_tc_button($buttons) {
    array_push($buttons, "nto_shortcode_button1");
    return $buttons;
}

Then, when initiating my post type:

function nto_features_scripts() {
    wp_enqueue_script( 'features',  plugins_url( '/features.js', __FILE__ ), array(), 'false', true );
}
add_action( 'admin_head', 'nto_features_scripts', 100 );

Then finally, in features.js:

tinymce.init({
    selector: "textarea",
    toolbar: "mybutton",
    setup: function(editor) {
        editor.addMenuItem('myitem', {
            text: 'My menu item',
            context: 'nto_shortcode_button1',
            onclick: function() {
                editor.insertContent('Some content');
            }
        });
    }
});

Returns:

Uncaught ReferenceError: tinymce is not defined

Q: How can I correctly initiate this addition to my custom button?