回调函数返回未定义值

Question

我正在尝试使用 Google 地图 API 来 return 从一个点到另一个点的旅程时间和长度。这是我的代码。

var routeInfoObject;

function findRoutes(given_origin, given_destination){
  var directionsService = new google.maps.DirectionsService();

  var directionsRequest = {
    origin: given_origin,
    destination: given_destination,
    travelMode: google.maps.DirectionsTravelMode.WALKING,
    unitSystem: google.maps.UnitSystem.METRIC,
    provideRouteAlternatives: true
  };

  var times = new Array();
  var lengths = new Array();
  var positions = new Array();
  directionsService.route(directionsRequest, function(response, status) {
      if (status == google.maps.DirectionsStatus.OK) {
         for (i = 0; i < response.routes.length && i < 4 ; i++) 
         {
             times[i] = response.routes[i].legs[0].duration.text;
             lengths[i] = response.routes[i].legs[0].distance.text;
         }

         routeInfoObject = times;
      } else { 
         console.log("There was an error with the request") 
      }
  });

  console.log(routeInfoObject);
}

底部的日志总是return未定义，即使 routeInfoObject 是一个全局变量并且应该设置为时间值。如果我运行 findRoutes("longsight","rusholme") returns [18,18,18].

在回调函数中记录时间值

Answer 1

回调函数 (function(response, status)) 直到在您的 console.log 语句后才执行，因此 尚未分配.

回调函数返回未定义值

Callback function returning undefined value

javascript

callback

undefined