Leaflet獲取可視范圍內4個頂點

//地圖級別改變時發生
map.on("zoomend", function (e) {
var zoom_val = e.target.getZoom();
map_drag();;
});
//拖動地圖時發生
map.on("moveend", function (e) {
map_drag();;
});

function map_drag() {
//左下角坐標（西南方）
var leftdown = map.getBounds().getSouthWest().lng + "," + map.getBounds().getSouthWest().lat;
L.circleMarker([map.getBounds().getSouthWest().lat, map.getBounds().getSouthWest().lng], { fillColor: "#f00", radius: 10 }).bindLabel("左下角坐標" + leftdown, { direction: 'right', noHide: true }).addTo(map);
//右上角坐標（東北方向）
var rightdown = map.getBounds().getNorthEast().lng + "," + map.getBounds().getNorthEast().lat;
L.circleMarker([map.getBounds().getNorthEast().lat, map.getBounds().getNorthEast().lng], { fillColor: "#f00", radius: 10 }).bindLabel("右上角坐標" + rightdown, { direction: 'left', noHide: true }).addTo(map);
//var strText = "當前地圖級別：" + zoom_val + " 左下角坐標：" + leftdown + " 右下角坐標：" + rightdown;
//左上角：西北方
var leftdown = map.getBounds().getNorthWest().lng + "," + map.getBounds().getNorthWest().lat;
L.circleMarker([map.getBounds().getNorthWest().lat, map.getBounds().getNorthWest().lng], { fillColor: "#f00", radius: 10 }).bindLabel("左上角坐標" + leftdown, { direction: 'right', noHide: true }).addTo(map);

//右下角：東南方
var leftdown = map.getBounds().getSouthEast().lng + "," + map.getBounds().getSouthEast().lat;
L.circleMarker([map.getBounds().getSouthEast().lat, map.getBounds().getSouthEast().lng], { fillColor: "#f00", radius: 10 }).bindLabel("右下角坐標" + leftdown, { direction: 'left', noHide: true }).addTo(map);

}