Add Custom Widgets to WordPress Sidebar Easily

Code

<?php
// Register and load the widget
function wp_dudecom_load_custom_widget() {
    register_widget('wp_dudecom_custom_widget');
}
add_action('widgets_init', 'wp_dudecom_load_custom_widget');

// Creating the widget class
class wp_dudecom_custom_widget extends WP_Widget {

    // Construct the widget
    function __construct() {
        parent::__construct(
            'wp_dudecom_custom_widget', // Base ID
            __('WP DudeCom Custom Widget', 'wp_dudecom_domain'), // Name
            array('description' => __('A Custom Widget for WP DudeCom', 'wp_dudecom_domain'),) // Args
        );
    }

    // Creating the widget front-end
    public function widget($args, $instance) {
        $title = apply_filters('widget_title', $instance['title']);
        
        // Before and after widget arguments are defined by themes
        echo $args['before_widget'];
        if (!empty($title))
            echo $args['before_title'] . $title . $args['after_title'];

        // This is where you run the code and display the output
        echo __('Hello, World!', 'wp_dudecom_domain');
        echo $args['after_widget'];
    }

    // Widget Backend
    public function form($instance) {
        if (isset($instance['title'])) {
            $title = $instance['title'];
        } else {
            $title = __('New title', 'wp_dudecom_domain');
        }
        // Widget admin form
        ?>
        <p>
            <label for="<?php echo esc_attr($this->get_field_id('title')); ?>"><?php _e('Title:'); ?></label>
            <input class="widefat" id="<?php echo esc_attr($this->get_field_id('title')); ?>" name="<?php echo esc_attr($this->get_field_name('title')); ?>" type="text" value="<?php echo esc_attr($title); ?>" />
        </p>
        <?php
    }

    // Updating widget replacing old instances with new
    public function update($new_instance, $old_instance) {
        $instance = array();
        $instance['title'] = (!empty($new_instance['title'])) ? sanitize_text_field($new_instance['title']) : '';
        return $instance;
    }
}
?>