Custom Widget Register

custom-widget-register.php

<?php
// Creating the widget 
class bs_custom_widget extends WP_Widget
{
    
    function __construct()
    {
        parent::__construct(
        // Base ID of your widget
            'bs_custom_widget', 
        // Widget name will appear in UI
            __('BackStrap Custom Widget', 'textdomain'), 
        // Widget description
            array(
            'description' => __('Sample widget based description here', 'textdomain')
        ));
    }
    
    // Creating widget front-end
    // This is where the action happens
    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!', 'textdomain');
        echo $args['after_widget'];
    }
    
    // Widget Backend 
    public function form($instance)
    {
        if (isset($instance['title'])) {
            $title = $instance['title'];
        } else {
            $title = __('New title', 'textdomain');
        }
        // Widget admin form
?>
<p>
<label for="<?php
        echo $this->get_field_id('title');
?>"><?php
        _e('Title:');
?></label> 
<input class="widefat" id="<?php
        echo $this->get_field_id('title');
?>" name="<?php
        echo $this->get_field_name('title');
?>" type="text" value="<?php
        echo esc_attr($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'])) ? strip_tags($new_instance['title']) : '';
        return $instance;
    }
} // Class bs_custom_widget ends here

// Register and load the widget
function bs_load_widget()
{
    register_widget('bs_custom_widget');
}
add_action('widgets_init', 'bs_load_widget');