循环中的异步函数运行速度太慢.我该如何提高表现

在我正在开发的应用程序中，我用鼠标点击谷歌地图绘制了一个圆圈。鼠标单击设置圆心。这个圆的半径是0.5英里。通过使用brandanee的node-gtfs，我进行异步调用以查找半径0.5英里内的路线。每个圆圈通常有多条路线。然后，我在每个路线上为这个圆圈内的一个方向（仅限南行或北行）的最近公交车站做了标记。问题是；它工作缓慢。我将findClosestStop函数的时间复杂度从n更改为log(n)，希望它能产生显著的影响。它起到了作用，但仍然需要4到10秒才能放置所有标记，这取决于附近路线的数量。这是我使用NodeJS和AngularJS的第一个项目。在这个项目之前，我只熟悉JavaScript的语法。我想知道我能做些什么来使这项工作更快？我是不是犯了一个概念错误？当我等待答案时，我会将（查找最近的停止）功能移到后端，看看它是否会对性能产生影响，尽管我不这么认为，因为会有相同的计算量。

如果你需要更多信息，请告诉我。期待听到对此的一些反馈。提前谢谢。

controller.js

    ...
        var distance = new distance.Distance();
    ...
        function createGTFSCluster(name, lat, lng, walk, bike, map) {
            var deferred = $q.defer();
            var clusterCenter = new graph.Center(lat, lng, map);
            var cluster = new graph.NodeCluster(clusterCenter, walkRadius, bikeRadius);
            cluster.setName(name);
            getRoutesNearby(cluster.clusterCenter, cluster.bikeRadius)
                .then(function(results) {
                    // Set the cluster's nearby routes
                    var routes = results[0];
                    cluster.nearbyRoutes = routes;
                    angular.forEach(routes, function(route, index){
                        getStopsByRoute(agency_key,route.route_id, 1).then(function(json){
                                            console.log(index, '->', route.route_id);
                            var stops = json[0];
                            var closestStop = distance.getClosestStop(stops, cluster);
                            cluster.setNodes(closestStop, route);
                        })
                    });
                        // Set the cluster's nodes to the stops found
                        deferred.resolve(cluster);
                });
            return deferred.promise;
        }
    ...

    // Retrieves the routes near a certain point on the map
        //
        // Input: cluster - A node cluster on the map we are finding routes for
        // Output: A promise whose results are the nearby route IDs
        function getRoutesNearby(center, radius) {
            var deferred = $q.defer();
            // Query the GTFS service for nearby routes and draw them
            gtfs.getRoutesByLocation(agency_key, center.lat, center.lon, radius)
                .then(function(json) {
                    //Get all route objects not only IDs
                    var routes = [];
                    for(index in json){
                        routes.push(json[index]);
                    }
                    // We got the routes, resolve
                    deferred.resolve(routes);
                });
            return deferred.promise;
        }
...
    function getStopsByRoute(agency_key, route_id, direction_id){
        var deferred = $q.defer();
        gtfs.getStopsByRoute(agency_key, route_id, direction_id)
            .then(function(json){ //all stops on the route in one direction
                var stopsArr =[];
                stopsArr.push(json.data[0].stops);
                deferred.resolve(stopsArr);
            });
            return deferred.promise;
    }

距离.js

    Distance.prototype.getClosestStop = function (stops, cluster){
      var closestStop = findClosestStop(stops, cluster);
      return closestStop;
    }
  function findDistance(stopObj, clusterObj){
    var stopCenter = {
      lat:stopObj.stop_lat,
      lon:stopObj.stop_lon
    };
    var clusterCenter = clusterObj.clusterCenter;
    var lat1 = stopCenter.lat;
    var lat2 = clusterCenter.lat;
    var lon1 = stopCenter.lon;
    var lon2 = clusterCenter.lon;
    var x1 = lat2 - lat1;
    var x2 = lon2 - lon1;
    var dLat = toRadians(x1);
    var dLon = toRadians(x2);
    var R = 3958.756; // miles
    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
                  Math.cos(toRadians(lat1)) * Math.cos(toRadians(lat2)) *
                  Math.sin(dLon/2) * Math.sin(dLon/2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    var d = R * c;
    return d;
  }

function toRadians(number){
  var inRadian = number * Math.PI / 180;
//  console.log('number->', number, 'inRadian->', inRadian);
  return inRadian;
}

     function findClosestStop(stops, cluster){
       //set new indeces
      var startIndex = 0;
      var endIndex = stops.length-1;
      //set new stop objects
      var firstStop = stops[startIndex];
      var lastStop = stops[endIndex];
      var closestStop;
      var returnIndex = 0;
      //dS: distance between the first stop and the cluster Center
      //dE: distance between the last stop and the cluster center
      var dS = findDistance(firstStop, cluster);
      var dE = findDistance(lastStop, cluster);
      if (dS > dE){
        startIndex = startIndex+endIndex / 2;
        returnIndex = 1;
      }
      if(dE > dS){
        endIndex = startIndex+endIndex / 2;
        returnIndex = 0;
      }
      if(stops.length > 2){
        stops = stops.slice(startIndex,(endIndex+1));
        return findClosestStop(stops, cluster);
      }else if(stops.length === 2){
        return stops[returnIndex];
      }else{
        return stops[0];
      }
    }