从数组中删除 JSON 中不存在的项目

Question

我得到 JSON 数据：

[
  {"id":'1029',
    "position":
        {
        "lat":'40.690902',
        "long":'-73.993449'
        }
  }
]

然后处理数据并将每个标记添加到myMarkers 并创建一个标记，或者如果它已经存在，则更新地图上的位置：

// Remember markers
var myMarkers = {};

***// Code removed here which gets JSON via ajax //***

// Move data to res variable, just for fun..
var res = data;

// Process the data..
for(var i=0, len=res.length; i<len; i++) {

    // Does this marker exist?
    if(myMarkers.hasOwnProperty(res[i].id)) {

        // Update position
        myMarkers[res[i].id].setPosition(new google.maps.LatLng(res[i].position.lat,res[i].position.long));

    } else {
    // It does NOT exist, create it ..

        var marker = new google.maps.Marker({
            position: new google.maps.LatLng(res[i].position.lat,res[i].position.long),
            map:map,
        });    

        myMarkers[res[i].id] = marker;

    }   

}

到目前为止，一切都很好。现在，我遇到了 JSON 数据可能缺少一些之前创建的并且已经在地图上的项目的问题。在这种情况下，我希望它们完全从myMarkers 中删除并从地图上擦除。我无法理解如何实现这一目标。有什么建议吗？

更新：

我尝试了以下方法来“反转”该过程，但它似乎不起作用，即使它是有意义的（至少对我而言）：

for(var i=0, len=myMarkers.length; i<len; i++) {
                console.log("Checking reverse..");

                    //Do we have this marker already?
                    if(data.hasOwnProperty(res[i].id)) {

                        console.log(res[i].id+" exists ..");
                        // Remove it here..

                    } else {

                        console.log(res[i].id+" does NOT exist ..");
                        // Do nothing

                    }


                }

我确定我只是错了一点，但我不知道在哪里。

Answer 1

我创建了一个示例代码 sn-p，它展示了如何从 myMarkersobject 中删除 JSON 数组 dataJSON 中不存在的标记

let dataJSON = [
  {
  	"id":'1',
    "position":
        {
        "lat":'40.690902',
        "long":'-73.993449'
        }
  },
  {
  	"id":'3',
    "position":
        {
        "lat":'40.690902',
        "long":'-74.993449'
        }
  },
  {
  	"id":'5',
    "position":
        {
        "lat":'41.690902',
        "long":'-73.993449'
        }
  }
];

let myMarkers = {
	'1': new Object(),
  '2': new Object(),
  '3': new Object(),
  '4': new Object(),
  '5': new Object()
};

let idsFromJSON = dataJSON.map(jsonElem => jsonElem.id);
console.log("IDs from JSON");
console.log(idsFromJSON);

let idsFromMarkers = Object.getOwnPropertyNames(myMarkers);
console.log("IDs from myMarkers");
console.log(idsFromMarkers);

let jsonSet = new Set(idsFromJSON);
let markersSet = new Set(idsFromMarkers);

let difference = new Set(
    [...markersSet].filter(x => !jsonSet.has(x)));

difference.forEach(id => {
		//First you should delete marker from map
    //myMarkers[id].setMap(null);  //commented as we don't have real instances in this example
    //Now delete marker from hash
    delete myMarkers[id];
});

console.log("Markers after delete");
console.log(myMarkers);

我希望这会有所帮助！