WordPress widget - linked image for sidebar

sidebarBanner.php

<?php
/** 
*  Steps:
*  1. Pop this in your theme's functions.php file
*  2. See the other gist for JS instructions
*  3. Profit
*/

// Register widget area.
function sidebar_widgets_init() {
	register_sidebar([
		'name' => 'Sidebar Banner Widget',
		'id' => 'sidebar_banner_widget',
		'before_widget' => '<div class="widget editorial-aside">',
		'after_widget' => '</div>',
		'before_title' => '<h2>',
		'after_title' => '</h2>'
	]);
}

add_action('widgets_init', 'sidebar_widgets_init');

// Register widgets.
class Banner_Widget extends WP_Widget {
	public function __construct() {
		$widget_ops = [
			'classname' => 'sidebar_banner_widget',
			'description' => 'Displays a linked banner image in the sidebar'
		];
		
		// Set up widget parameters.
		parent::__construct('sidebar_banner_widget', 'Banner Widget', $widget_ops);

		// Add Widget scripts
		add_action('admin_enqueue_scripts', array($this, 'scripts'));
	}

	// Enqueue scripts
	public function scripts()
	{
		wp_enqueue_script('media-upload');
		wp_enqueue_media();
		wp_enqueue_script('widgets', get_template_directory_uri() . '/assets/js/widgets.js', array('jquery'));
	}

	// Output widget content.
	public function widget($args, $instance) {
		// Only echo the widget contents if all required instance parameter values are present.
		if($instance['image'] && $instance['link']):
			// Set alt string.
			$alt_string = ! empty($instance['image_alt_text']) ? $instance['image_alt_text'] : '';

			echo $args['before_widget'];
			echo $args['before_title'] . apply_filters('widget_title', $instance['title'] ) . $args['after_title'];
			echo '<a href="'. $instance['link'] .'"><img src="'. esc_url($instance['image']) .'" alt="'. $alt_string .'"></a>';
			echo $args['after_widget'];
   endif;
	}

	// Admin form output.
	public function form($instance) {
		$link = !empty($instance['link']) ? $instance['link'] : esc_html__('https://', 'text_domain');
		$image = !empty($instance['image']) ? $instance['image'] : '';
		$image_alt_text = !empty($instance['image_alt_text']) ? $instance['image_alt_text'] : esc_html__('', 'text_domain');
		?>
			<p>
				<label for="<?php echo esc_attr($this->get_field_id('link')); ?>"><?php esc_attr_e('Link:', 'text_domain'); ?></label> 
				<input class="widefat" id="<?php echo esc_attr($this->get_field_id('link')); ?>" name="<?php echo esc_attr($this->get_field_name('link')); ?>" type="text" value="<?php echo esc_attr($link); ?>">
			</p>
			<p>
			<label for="<?php echo $this->get_field_id( 'image' ); ?>"><?php echo 'Image:'; ?></label>
      	<input class="widefat" id="<?php echo $this->get_field_id('image'); ?>" name="<?php echo $this->get_field_name('image'); ?>" type="text" value="<?php echo esc_url($image); ?>" />
      <button class="upload_image_button button button-primary" style="margin-top: 5px;">Upload Image</button>
			</p>
			<p>
				<label for="<?php echo esc_attr($this->get_field_id('image_alt_text')); ?>"><?php esc_attr_e('Image Alt Text (optional):', 'text_domain'); ?></label> 
				<input class="widefat" id="<?php echo esc_attr($this->get_field_id('image_alt_text')); ?>" name="<?php echo esc_attr($this->get_field_name('image_alt_text')); ?>" type="text" value="<?php echo esc_attr($image_alt_text); ?>">
			</p>
		<?php 
	}

	// Process widget options on save.
	public function update ($new_instance, $old_instance) {
		$instance = array();
		$instance['title'] = (! empty($new_instance['title'])) ? sanitize_text_field($new_instance['title']) : '';
		$instance['link'] = (! empty($new_instance['link'])) ? sanitize_text_field($new_instance['link']) : '';
		$instance['image'] = (! empty( $new_instance['image'])) ? $new_instance['image'] : '';
		$instance['image_alt_text'] = (! empty( $new_instance['image_alt_text'])) ? $new_instance['image_alt_text'] : '';

		return $instance;
	}
}

add_action('widgets_init', function() {
	register_widget('Banner_Widget');
});