Source: bemap-leaflet/bemap-map-leaflet-circle.js

/**
 * Add a bemap.Circle to the layer
 * @public
 * @param {bemap.Circle} bemap.Circle.
 * @param {object} options
 * @return {bemap.LeafletMap}
 */
bemap.LeafletMap.prototype.addCircle = function(circle, options) {
  if (circle && bemap.inheritsof(circle, bemap.Circle)) {
    var style = circle.getStyle();
    var fillColor = style.getFillColor();
    var borderColor = style.getBorderColor();

    circle.native = L.circle(circle.getCoordinate().getLatLonArray(), circle.getRadius(), {
      fillColor: fillColor.getHex(),
      opacity: fillColor.getAlpha(),
      color: borderColor.getHex(),
      weight: style.getBorderWidth(),
    });

    if (circle.map === null) {
      circle.map = this;
    }

    var opts = options || {};
    var l = null;

    if (opts.layer !== undefined && (bemap.inheritsof(opts.layer, bemap.VectorLayer))) {
      l = opts.layer;
    } else {
      l = this.getLayerByName(bemap.Map.DEFAULT_LAYER.CIRCLE);
      if (l === null) {
        l = new bemap.VectorLayer({
          name: bemap.Map.DEFAULT_LAYER.CIRCLE
        });
        this.addLayer(l);
      }
    }

    if (circle.layer === null) {
      circle.layer = l;
    }

    circle.native.addTo(l.native);
  }

  return this;
};

/**
 * Set the coordinates of the circle.
 * @protected
 * @param {bemap.Circle} circle the circle object to remove.
 * @return {bemap.LeafletMap} this
 */
bemap.LeafletMap.prototype.setCoordinateCircle = function(circle) {
  var c = circle.getCoordinate();
  circle.native.setLatLng(L.latLng(c.getLat(), c.getLon()));
  return this;
};

/**
 * Set the radius of the circle.
 * @protected
 * @param {bemap.Circle} circle the circle object to remove.
 * @return {bemap.LeafletMap} this
 */
bemap.LeafletMap.prototype.setRadiusCircle = function(circle) {
  circle.native.setRadius(circle.getRadius());
  return this;
};

/**
 * Remove a circle from his layer.
 * @public
 * @param {bemap.Circle} circle the circle object to remove.
 */
bemap.LeafletMap.prototype.removeCircle = function(circle) {
  if (circle && circle.layer && circle.layer.native && bemap.inheritsof(circle, bemap.Circle)) {
    circle.map.native.removeLayer(circle.native);
    circle.layer = null;
    circle.map = null;
  }
  return this;
};

/**
 * Set the listner when an specified eventType occur on bemap.Circle.
 * @public
 * @param {bemap.Circle} circle
 * @param {bemap.Map.EventType} eventType Event type.
 * @param {function} callback Function will be called when the specified eventType is occur.
 * @param {object} options options.
 * @return {bemap.Listener} this.
 */
bemap.LeafletMap.prototype.onCircle = function(circle, eventType, callback, options) {

  var opts = options ? options : {};

  var nativeListener = circle.native.on(eventType, function(evt) {
    var mapEvent = new bemap.MapEvent({
      native: evt,
      bemapObject: circle,
      x: evt.containerPoint ? evt.containerPoint.x : undefined,
      y: evt.containerPoint ? evt.containerPoint.y : undefined,
      coordinate: evt.latlng ? new bemap.Coordinate(evt.latlng.lng, evt.latlng.lat) : undefined,
      properties: options,
      map: this
    });
    callback(mapEvent);
  });
  var listener = new bemap.Listener({
    native: nativeListener,
    callback: callback,
    key: eventType,
    bemapObject: circle
  });

  return listener;
};

/**
 * Define the draggable capability for bemap.Circle.
 * @protected
 * @param {bemap.Circle} circle bemap object.
 * @param {function} callback Function will be called when the specified eventType is occur.
 * @param {object} options Options.
 * @param {bemap.Layer} options.layerFilter set the bemap layer used as filter.
 * @return {bemap.Listener} bemap.listener.
 */
bemap.LeafletMap.prototype.draggableCircle = function(circle, callback, options) {
  var _this = this,
    opts = options ? options : {},
    startPixel, startCoordinate;

  circle.native.on('mousedown', function(evt) {
    _this.native.dragging.disable();
    startPixel = evt.containerPoint;

    var latlng = circle.native._latlng;
    var circleStartingLat = latlng.lat;
    var circleStartingLng = latlng.lng;

    startCoordinate = new bemap.Coordinate(circleStartingLng, circleStartingLat);

    latlng = evt.latlng;
    var mouseStartingLat = latlng.lat;
    var mouseStartingLng = latlng.lng;

    _this.native.on('mousemove', function(evt) {
      latlng = evt.latlng;
      var mouseNewLat = latlng.lat;
      var mouseNewLng = latlng.lng;

      var latDifference = mouseStartingLat - mouseNewLat;
      var lngDifference = mouseStartingLng - mouseNewLng;
      var center = [circleStartingLat - latDifference, circleStartingLng - lngDifference];
      circle.native.setLatLng(center);
    });
  });

  this.native.on('mouseup', function(evt) {
    _this.native.dragging.enable();
    _this.native.removeEventListener('mousemove');

    var mapEvent = new bemap.MapEvent({
      native: evt,
      bemapObject: circle,
      x: evt.containerPoint ? evt.containerPoint.x : undefined,
      y: evt.containerPoint ? evt.containerPoint.y : undefined,
      coordinate: evt.latlng ? new bemap.Coordinate(evt.latlng.lng, evt.latlng.lat) : undefined,
      //startX: startPixel.x,
      //startY: startPixel.y,
      //startCoordinate: startCoordinate,
      properties: options,
      map: this
    });

    callback(mapEvent);
  });

  this.events.dragFeature = new bemap.Listener({
    native: null,
    key: "dragFeature",
    bemapObject: circle
  });

  return this.events.dragFeature;
};