默认情况下，文档完成加载后无法加载该API，您需要异步加载该API。
用地图修改页面：
<div id="map_canvas" ></div><script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script><script src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false&callback=initialize"></script><script>var directionsDisplay, directionsService, map;function initialize() { var directionsService = new google.maps.DirectionsService(); directionsDisplay = new google.maps.DirectionsRenderer(); var chicago = new google.maps.LatLng(41.850033, -87.6500523); var mapOptions = { zoom:7, mapTypeId: google.maps.MapTypeId.ROADMAP, center: chicago } map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions); directionsDisplay.setMap(map);}</script>
