如何使用javascript检查变量是否在内存中答案

【问题标题】：how to check the Variable is or not in the Memory using javascript如何使用javascript检查变量是否在内存中
【发布时间】：2010-10-19 10:41:56
【问题描述】：

当我放大地图但看不到标记时，我想检查标记（谷歌地图 v3）是否在内存中。

那我该怎么办，

【问题讨论】：

标签： javascript google-maps memory google-maps-markers

【解决方案1】：

您需要以数组的形式跟踪添加到地图的标记。您需要添加一个 bounds_changed 事件侦听器，其中包含一个搜索该数组并检查标记坐标是否在地图范围内的函数。例如：

<html>
    <head>
        <script type="text/javascript" src= "http://maps.google.com/maps/api/js?sensor=false">
        </script>
        <script>

            var map;
            markers = [];
            function initialize(){
                geocoder = new google.maps.Geocoder();
                var latlng = new google.maps.LatLng(-34.397, 150.644);
                var myOptions = {
                    zoom: 8,
                    center: latlng,
                    mapTypeId: google.maps.MapTypeId.ROADMAP
                }
                map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);

                //if creating multiple markers you would do marker creation and storage in a loop
                var marker1 = new google.maps.Marker({
                    map: map,
                    position: latlng,
                    title: "Marker 1"
                });
                var marker2 = new google.maps.Marker({
                    map: map,
                    position: new google.maps.LatLng(-34.2, 150.644),
                    title: "Marker 2"
                });
                //save your marker to an array to keep track of your markers - i am assuming all markers are initially visible
                markers.push({
                    visible: true,
                    marker: marker1
                })
                markers.push({
                    visible: true,
                    marker: marker2
                })

                //watch for zoom change event
                google.maps.event.addListener(map, 'bounds_changed', function(){
                    checkBounds()

                })

            }

            function checkBounds(){

                //get bounds for a new zoom level
                bounds = map.getBounds();
                //loop through markers array to check if they are still in bounds (visible)
                for (i = 0; i < markers.length; i++) {
                   m = markers[i].marker
                    if (bounds.contains(m.position)) {
                        //do something here for markers that are visible
                        markers[i].visible = true;
                    }
                    else {
                        //do something here for markers that are not visible
                        markers[i].visible = false;
                    }
                }
            }

            //this is just to show which markers are visible and which ones are not
            function show(){
                htmlVisible = ""
                htmlHidden = ""
                for (i = 0; i < markers.length; i++) {
                     m = markers[i].marker
                    if (markers[i].visible) {

                        htmlVisible += m.title + "\n";
                    }
                    else {
                        htmlHidden += m.title + "\n";
                    }

                }
                alert("Visible markers:\n" + htmlVisible + "\n" + "Markers out of bounds:\n" + htmlHidden)
            }
        </script>
    </head>
    <body onload="initialize()">
        <div id="map_canvas" style="width: 320px; height: 480px;">
        </div>
        <input type=button onclick="show()" value="List visible/out of bounds markers">
    </body>
</html>

【讨论】：