lubuntu.me/plugins/so-widgets-bundle/base/inc/fields/autocomplete.class.php

<?php

/**
 * Class SiteOrigin_Widget_Field_Autocomplete
 */
class SiteOrigin_Widget_Field_Autocomplete extends SiteOrigin_Widget_Field_Text_Input_Base {

	/**
	 * An array of post types to use in the autocomplete query. Only used for posts.
	 *
	 * @access protected
	 * @var array
	 */
	protected $post_types;

	/**
	 * Indicates which database table will be used to retrieve autocomplete suggestions.
	 * Currently only `posts` and `terms` are allowed.
	 *
	 * @access protected
	 * @var string
	 */
	protected $source;

	/**
	 * The CSS classes to be applied to the rendered text input.
	 */
	protected function get_input_classes() {
		return array( 'widefat', 'siteorigin-widget-input', 'siteorigin-widget-autocomplete-input' );
	}

	protected function get_default_options() {
		$defaults = parent::get_default_options();
		$defaults['source'] = 'posts';
		return $defaults;
	}

	protected function render_after_field( $value, $instance ) {
		$post_types = ! empty( $this->post_types ) && is_array( $this->post_types ) ? implode( ',', $this->post_types ) : '';
		?>
		<div class="existing-content-selector">

			<input type="text" class="content-text-search"
			       data-post-types="<?php echo esc_attr( $post_types ) ?>"
			       data-source="<?php echo esc_attr( $this->source ) ?>"
			       placeholder="<?php esc_attr_e( 'Search', 'so-widgets-bundle' ) ?>"/>

			<ul class="items"></ul>

			<div class="buttons">
				<a href="#" class="button-close button"><?php esc_html_e('Close', 'so-widgets-bundle') ?></a>
			</div>
		</div>
		<?php
		parent::render_after_field( $value, $instance );
	}

	function enqueue_scripts() {
		wp_enqueue_script( 'so-autocomplete-field', plugin_dir_url( __FILE__ ) . 'js/autocomplete-field' . SOW_BUNDLE_JS_SUFFIX .  '.js', array( 'jquery' ), SOW_BUNDLE_VERSION );
	}
}