在我正在处理的应用程序中，我在Google地图上单击鼠标即可绘制一个部分。鼠标单击设置圆的中心。圆的半径是0.5英里。使用brandannee's node-gtfs时，我会进行异步调用以查找0.5英里范围内的路径。每个圈子通常有多条路线。然后，我为每个路线上最近的公交车站设置了一个标记，仅用于该圈内的一个方向（仅限于南行或北行）。问题是;它运作缓慢。我将findClosestStop函数的时间复杂度从n更改为log(n)，希望它能产生显着差异。它有所不同但仍然需要4到10秒才能放置所有标记，这取决于路径附近的数量。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才能让这项工作更快？我犯了一个概念错误吗？当我等待答案时，我会将（找到最接近的停止）功能移动到后端，看看它是否会对性能产生影响，即使我不这么认为，因为会有相同数量的计算。
如果您需要更多信息，请与我们联系。期待听到一些关于此的反馈。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;
}
distance.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];
}
}
答案 0 :(得分：2)
你在哪里浪费时间？
我建议使用一些
console.time(timerName);
看看你在哪里浪费时间。如果您确切知道丢失的位置，那么分析会更容易。
对于客户端应用程序来说，105组数据应该没有问题。
现在我建议您在控制台中运行这两个代码段
此代码段计算您的角度摘要。只需将其放入您的控制台，然后使用您的应用程序。
(function monitorDigestCycle(angular) {
var injector = angular.element(document.body).injector();
if (!injector) {
throw new Error('Missing Angular injector on the document body');
}
var $rootScope = injector.get('$rootScope');
function dummy() {
console.count('digest cycle');
}
window.stopWatching = $rootScope.$watch(dummy);
console.log('run window.stopWatching() to stop watching the digest cycle');
}(window.angular));
或者这个片段。它包装了一个函数（您需要调整自己使用的代码片段）并记录函数调用的chrome profiler。这样便于分析。
(function profileScopeMethod() {
var selector = 'find';
var methodName = 'find';
var name = selector + ':' + methodName;
/* global angular */
var el = angular.element(document.getElementById(selector));
var scope = el.scope() || el.isolateScope();
console.assert(scope, 'cannot find scope from ' + name);
var fn = scope[methodName];
console.assert(typeof fn === 'function', 'missing ' + methodName);
var $timeout = el.injector().get('$timeout');
var $q = el.injector().get('$q');
scope[methodName] = function () {
console.profile(name);
console.time(name);
// method can return a value or a promise
var returned = fn();
$q.when(returned).finally(function finishedMethod() {
console.timeStamp('finished', methodName);
$timeout(function afterDOMUpdate() {
console.timeStamp('dom updated after', methodName);
console.timeEnd(name);
console.profileEnd();
scope[methodName] = fn;
console.log('restored', name);
}, 0);
});
};
console.log('wrapped', name, 'for measurements');
}());
在这里，您可以找到更多代码片段来分析角度应用
https://github.com/bahmutov/code-snippets