无法从函数中获取值

Question

我正在制作邻居地图的udacity项目，我必须在其中标记位置，当点击标记时，它应显示来自另一个API的信息。我能够从API获取数据但无法附加到我的信息块。下面我提供完整的代码：

当我尝试从第94行打电话时，我没有得到任何数组。我需要第96行的数据来附加信息框。我无法从popContent函数中获取数据。

var map;
var platform = new H.service.Platform({
    'app_id': 'app_id',
    'app_code': 'app_code'
});
// Obtain the default map types from the platform object:
var defaultLayers = platform.createDefaultLayers();
// Instantiate (and display) a map object:
var map = new H.Map(
    document.getElementById('map'),
    defaultLayers.normal.map,
    {
        zoom: 10,
        center: { lat: 19.0760, lng: 72.8777 }
    });
// Create the default UI:
var ui = H.ui.UI.createDefault(map, defaultLayers);
// MapEvents enables the event system
// Behavior implements default interactions for pan/zoom (also on mobile touch environments)
var behavior = new H.mapevents.Behavior(new H.mapevents.MapEvents(map));
//data for marker
var Location = function(title,lat, lng){
    var self = this;
    this.title = title;
    this.lat = lat;
    this.lon = lng;
    //get content of marker location
    this.popContent = function(newtitle,newlat,newlon){
        var markerarray = [];
        var foursquareURL = 'https://api.foursquare.com/v2/venues/search?ll='+newlat+','+newlon+'&client_id=&client_secret=&v=20180908&query='+newtitle+'';
        //Using Foursquare API to get info about the restaurant
        $.getJSON(foursquareURL).done(function(data) {
            var results = data.response.venues[0];
            self.name = results.name;
            self.street = results.location.formattedAddress[0];
            self.city = results.location.formattedAddress[1]; 
            self.postalCode  = results.location.postalCode;
            markerarray.push(self.name,self.street,self.city,self.postalCode);
        }).fail(function() {
            alert("There was an error with the Foursquare API call. Please refresh the page and try again to load Foursquare data.");
        }); 
        return markerarray;
    };
    //info window
    this.addMarkerToGroup = function (group, coordinate, html) {
        var marker = new H.map.Marker(coordinate);
        // add custom data to the marker
        marker.setData(html);
        group.addObject(marker);
    };
    //open infowindow for location marker
    this.openinfowindow = function(map) {
        var group = new H.map.Group();
        map.addObject(group);
        // add 'tap' event listener, that opens info bubble, to the group
        group.addEventListener('tap', function (evt) {
            // event target is the marker itself, group is a parent event target
            // for all objects that it contains
            var bubble =  new H.ui.InfoBubble(evt.target.getPosition(), {
                // read custom data
                content: evt.target.getData()
            });
            // show info bubble
            ui.addBubble(bubble);
        }, false);
        var datahtml =  this.popContent(this.title,this.lat,this.lon);
        this.addMarkerToGroup(group, {lat:this.lat, lng:this.lon},'<div><a href="#" >'+datahtml[0]+'</a>' + '</div><div >'+datahtml[1]+'<br>' + datahtml[2]+'<br>'+datahtml[3]+'</div>');
    };
    this.openinfowindow(map);
    //assign click event for marker
};
var locationsModel = {
    //array
    locations:[
        new Location('Kanjurmarg',19.1317,72.9352),
        new Location('Thane', 19.2183, 72.9781),
        new Location('Powai', 19.1197, 72.9051),
        ],
        query: ko.observable(''),
};
// Search function for filtering through the list of locations based on the name of the location.
locationsModel.search = ko.dependentObservable(function() {
    var self = this;
    var search = this.query().toLowerCase();
    return ko.utils.arrayFilter(self.locations, function(location) {
        return location.title.toLowerCase().indexOf(search) >= 0;
    });
}, locationsModel);
//search function  for filtering locations
ko.applyBindings(locationsModel);

#map{
	height: 400px;
	width:100%;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<!DOCTYPE html>
<html>
<head>
	<title>Neighborhood project</title>
	<!-- optimum performance on mobile device -->
	<meta name="viewport" content="initial-scale=1.0, width=device-width" />
	<!-- loads the module -->
	<script src="http://js.api.here.com/v3/3.0/mapsjs-core.js"
	  type="text/javascript" charset="utf-8"></script>
	<script src="http://js.api.here.com/v3/3.0/mapsjs-service.js"
	  type="text/javascript" charset="utf-8"></script>
	<script src="http://js.api.here.com/v3/3.0/mapsjs-ui.js" 
	      type="text/javascript" charset="utf-8"></script>
	<link rel="stylesheet" type="text/css" 
	      href="http://js.api.here.com/v3/3.0/mapsjs-ui.css" />
	<script type="text/javascript" src="https://js.api.here.com/v3/3.0/mapsjs-mapevents.js"></script>
    <!-- custom stylesheet -->
	  <link rel="stylesheet" type="text/css" href="css/style.css">

</head>
<body>
   <h2>Neighborhood Maps</h2> 
    <div id="map"></div>
    


    <div class="search-area" id="search-area">
        <input class="search-input" placeholder="Search for Places..." type="text" name="q" data-bind="value: query, valueUpdate: 'keyup'">
        <ul class="location-list" data-bind="visible:query, template: {name: 'location', foreach: search}">
        </ul>
      </div>


<script
  src="https://code.jquery.com/jquery-3.3.1.js"
  integrity="sha256-2Kok7MbOyxpgUVvAk/HJ2jigOSYS2auK4Pfzbm7uH60="
  crossorigin="anonymous"></script>


<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>

 <script src="js/knockout-3.4.2.js" charset="utf-8"></script>

<script src="js/test.js"></script>
</body>
</html>

Answer 1

这是因为$.getJSON中的popContent是异步的，它不会立即返回值。在你的代码中，this.popContent()将始终返回空数组。

您需要做的是使您的代码依赖于$.getJSON响应。第一种方法是将所有内容包装在$.getJSON的回调中。第二种方式是使用承诺。