WP_Widget_Categories::widget( array $args, array $instance )

	public function widget( $args, $instance ) {
		static $first_dropdown = true;

		$title = ! empty( $instance['title'] ) ? $instance['title'] : __( 'Categories' );

		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
		$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

		$c = ! empty( $instance['count'] ) ? '1' : '0';
		$h = ! empty( $instance['hierarchical'] ) ? '1' : '0';
		$d = ! empty( $instance['dropdown'] ) ? '1' : '0';

		echo $args['before_widget'];

		if ( $title ) {
			echo $args['before_title'] . $title . $args['after_title'];
		}

		$cat_args = array(
			'orderby'      => 'name',
			'show_count'   => $c,
			'hierarchical' => $h,
		);

		if ( $d ) {
			echo sprintf( '<form action="%s" method="get">', esc_url( home_url() ) );
			$dropdown_id = ( $first_dropdown ) ? 'cat' : "{$this->id_base}-dropdown-{$this->number}";
			$first_dropdown = false;

			echo '<label class="screen-reader-text" for="' . esc_attr( $dropdown_id ) . '">' . $title . '</label>';

			$cat_args['show_option_none'] = __( 'Select Category' );
			$cat_args['id'] = $dropdown_id;

			/**
			 * Filters the arguments for the Categories widget drop-down.
			 *
			 * @since WP-2.8.0
			 * @since WP-4.9.0 Added the `$instance` parameter.
			 *
			 * @see wp_dropdown_categories()
			 *
			 * @param array $cat_args An array of Categories widget drop-down arguments.
			 * @param array $instance Array of settings for the current widget.
			 */
			wp_dropdown_categories( apply_filters( 'widget_categories_dropdown_args', $cat_args, $instance ) );

			echo '</form>';
			?>

<script type='text/javascript'>
/* <![CDATA[ */
(function() {
	var dropdown = document.getElementById( "<?php echo esc_js( $dropdown_id ); ?>" );
	function onCatChange() {
		if ( dropdown.options[ dropdown.selectedIndex ].value > 0 ) {
			dropdown.parentNode.submit();
		}
	}
	dropdown.onchange = onCatChange;
})();
/* ]]> */
</script>

<?php
		} else {
?>
		<ul>
<?php
		$cat_args['title_li'] = '';

		/**
		 * Filters the arguments for the Categories widget.
		 *
		 * @since WP-2.8.0
		 * @since WP-4.9.0 Added the `$instance` parameter.
		 *
		 * @param array $cat_args An array of Categories widget options.
		 * @param array $instance Array of settings for the current widget.
		 */
		wp_list_categories( apply_filters( 'widget_categories_args', $cat_args, $instance ) );
?>
		</ul>
<?php
		}

		echo $args['after_widget'];
	}