function flatten(array) {        return [].concat.apply([], array);    }    function polygonToLineString(coordinates, properties) {        return coordinates.map(function(coordinates) {            return turf.lineString(coordinates, properties);        });    }    function multiPolygonToLineString(coordinates, properties) {        return flatten(coordinates.map(function(coordinates) {            return polygonToLineString(coordinates, properties);        }));    }    function toLineString(feature) {        var geometry = feature.geometry,            properties = feature.properties;        switch (geometry.type) {            case 'Polygon':                return polygonToLineString(geometry.coordinates, properties);            case 'MultiPolygon':                return multiPolygonToLineString(geometry.coordinates, properties);            default:                return feature;        }    }    /**     * Transforms Polygons and MultiPolygons to LineStrings.     *     * @module turf/polygonToLine     * @category transformation     * @param {Object} geojson any GeoJSON object     * @returns {Object} FeatureCollection where     * Polygons and MultiPolygons transformed to LineStrings.     */    function polygon2line(geojson) {        var features = geojson.features.map(toLineString);        return turf.featureCollection(flatten(features));    }