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function load_scripts() {
wp_register_script( 'auto-complete-js', get_template_directory_uri() . '/js/jquery.auto-complete.min.js', array('jquery') );
wp_enqueue_script( 'auto-complete-js' );
}
//https://goodies.pixabay.com/jquery/auto-complete/demo.html
//https://github.com/Pixabay/jQuery-autoComplete


add_action('wp_ajax_nopriv_get_listing_names', 'ajax_listings');
add_action('wp_ajax_get_listing_names', 'ajax_listings');
// function apply_highlight($a_json, $parts) {

// 	$p = count($parts);
// 	$rows = count($a_json);

// 	for($row = 0; $row < $rows; $row++) {

// 		$label = $a_json[$row]["label"];
// 		$a_label_match = array();

// 		for($i = 0; $i < $p; $i++) {

// 			$part_len = mb_strlen($parts[$i]);
// 			$a_match_start = mb_stripos_all($label, $parts[$i]);

// 			foreach($a_match_start as $part_pos) {

// 				$overlap = false;
// 				foreach($a_label_match as $pos => $len) {
// 					if($part_pos - $pos >= 0 && $part_pos - $pos < $len) {
// 						$overlap = true;
// 						break;
// 					}
// 				}
// 				if(!$overlap) {
// 					$a_label_match[$part_pos] = $part_len;
// 				}

// 			}

// 		}

// 		if(count($a_label_match) > 0) {
// 			ksort($a_label_match);

// 			$label_highlight = '';
// 			$start = 0;
// 			$label_len = mb_strlen($label);

// 			foreach($a_label_match as $pos => $len) {
// 				if($pos - $start > 0) {
// 					$no_highlight = mb_substr($label, $start, $pos - $start);
// 					$label_highlight .= $no_highlight;
// 				}
// 				$highlight = '<span class="hl_results">' . mb_substr($label, $pos, $len) . '</span>';
// 				$label_highlight .= $highlight;
// 				$start = $pos + $len;
// 			}

// 			if($label_len - $start > 0) {
// 				$no_highlight = mb_substr($label, $start);
// 				$label_highlight .= $no_highlight;
// 			}

// 			$a_json[$row]["label"] = $label_highlight;
// 		}

// 	}

// 	return $a_json;

// }

function ajax_listings() {
	global $wpdb;


	$name = $wpdb->esc_like($_GET['term']).'%';

	$sql = "select id,post_title
		from $wpdb->posts
		where post_title like %s
		and post_type='city' and post_status='publish'";

	$sql = $wpdb->prepare($sql, $name);

	$results = $wpdb->get_results($sql);


	$a_json_row = array();
	foreach( $results as $r ) {


		$a_json_row[] = array(
			'id'      => $r->id,
			'value'      => $r->post_title,
			'label'      => $r->post_title

		);
	}


	$json = json_encode($a_json_row);
	echo $json;
	die();
}

<?php wp_footer() ?>
<script src="https://code.jquery.com/ui/1.10.0/jquery-ui.min.js"type="text/javascript"></script>

$("#city").autocomplete({

        source: "/wp-admin/admin-ajax.php?action=get_listing_names",
        minLength: 2,
        select: function(event, ui) {
            var url = ui.item.id;
            if(url != '#') {
                location.href = '/?post_type=city&p=' + url;
            }
        },

        html: true, // optional (jquery.ui.autocomplete.html.js required)

        // optional (if other layers overlap autocomplete list)
        open: function(event, ui) {
            $(".autocomplete").css("z-index", 1000);
        }
    });