How to create a custom dynamic WordPress widget?

class ts91_recent_post_widget extends WP_Widget 
{
 
 // The construct part of dynamic widget 
 function __construct() 
 {
  // construct code will go here
 }
   
 // Creating dynamic widget front-end
 public function widget( $args, $instance ) 
 {
  // dynamic widget front end will go here
 }
           
 // Creating dynamic widget Backend 
 public function form( $instance ) 
 {
  //admin form part will go here
 }
       
 // Updating dynamic widget replacing old instances with new
 public function update( $new_instance, $old_instance ) 
 {
  //this function will update the instance
 }
 
// Class ts91_widget ends here
}

//Registering the dynamic widget
function ts91_register_widget() 
{
    register_widget( 'ts91_recent_post_widget' );
}
add_action( 'widgets_init', 'ts91_register_widget' );

class ts91_recent_post_widget extends WP_Widget 
{
 
 // The construct part of dynamic widget 
 function __construct() 
 {
  parent::__construct(
  
  // Base ID of your widget
  'ts91_recent_post_widget', 
    
  // Widget name will appear in UI
  __('91 TechSquare Recent Posts', 'ts91_recent_post_widget_domain'), 
    
  // Widget description
  array( 'description' => __( 'custom dynamic widget based on 91 TechSquare Tutorial', 'ts91_recent_post_widget_domain' ), ) 
  );
 }
   
 // Creating dynamic widget front-end
 public function widget( $args, $instance ) 
 {
  $title = apply_filters( 'widget_title', $instance['title'] );
  $no_of_post = apply_filters( 'widget_number_of_post', $instance['number_of_post'] );
  
  // before and after widget arguments are defined by themes
  echo $args['before_widget'];
  if(empty($title))
  {
   $title = "91 TechSquare Recent Posts";
  }
  if ( ! empty( $title ) )
  echo $args['before_title'] . $title . $args['after_title'];

  
    
  // This is where you run the code and display the output
  $args = array(
         'posts_per_page' => $no_of_post, /* how many post you need to display */         'offset' => 0,
         'orderby' => 'post_date',
         'order' => 'DESC',
         'post_type' => 'post', /* your post type name */         'post_status' => 'publish'
     );
     $query = new WP_Query($args);
     if ($query->have_posts()) :
      echo "<ul>";
         while ($query->have_posts()) : $query->the_post();
             ?>
             <li>
             <a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
          </li>
             <?php
         endwhile;
         echo "</ul>";
     endif;
  echo $args['after_widget'];
 }
           
 // Creating dynamic widget Backend 
 public function form( $instance ) 
 {
  if ( isset( $instance[ 'title' ] ) ) {
  $title = $instance[ 'title' ];
  }
  else {
  $title = __( '91 TechSquare Recent Posts', 'ts91_recent_post_widget_domain' );
  }

  //getting number of post value to form
  if ( isset( $instance[ 'number_of_post' ] ) ) {
  $number_of_post = $instance[ 'number_of_post' ];
  }
  else {
  $number_of_post = 5;
  }
  // 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 ); ?>" />

  <label>No. of post:
  <input class="widefat" name="<?php echo $this->get_field_name( 'number_of_post' ); ?>" type="number" min="0" value="<?php echo esc_attr( $number_of_post ); ?>">
  </p>
  <?php
 }
       
 // Updating dynamic 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'] ) : '';
  $instance['number_of_post'] = ( ! empty( $new_instance['number_of_post'] ) ) ? strip_tags( $new_instance['number_of_post'] ) : '';
  return $instance;
 }
 
// Class ts91_widget ends here
}

//Registering the dynamic widget
function ts91_register_widget() 
{
    register_widget( 'ts91_recent_post_widget' );
}
add_action( 'widgets_init', 'ts91_register_widget' );