Adding Custom Options to Existing Widgets

adding-custom-options-existing-widgets.php

<?php
/* Displaying a Custom Widget Option */
function thmfdn_add_menu_description_option( $widget, $return, $instance ) {
 
    // Are we dealing with a nav menu widget?
    if ( 'nav_menu' == $widget->id_base ) {
 
        // Display the description option.
        $description = isset( $instance['description'] ) ? $instance['description'] : '';
        ?>
            <p>
                <input class="checkbox" type="checkbox" id="<?php echo $widget->get_field_id('description'); ?>" name="<?php echo $widget->get_field_name('description'); ?>" <?php checked( true , $description ); ?> />
                <label for="<?php echo $widget->get_field_id('description'); ?>">
                    <?php _e( 'Show descriptions', 'thmfdn_textdomain' ); ?>
                </label>
            </p>
        <?php
    }
}
add_filter('in_widget_form', 'thmfdn_add_menu_description_option', 10, 3 );

/* Saving a Custom Widget Option */
function thmfdn_save_menu_description_option( $instance, $new_instance ) {
 
    // Is the instance a nav menu and are descriptions enabled?
    if ( isset( $new_instance['nav_menu'] ) && !empty( $new_instance['description'] ) ) {
        $new_instance['description'] = 1;
    }
 
    return $new_instance;
}
add_filter( 'widget_update_callback', 'thmfdn_save_menu_description_option', 10, 2 );
?>