old_contents: import { polygon, featureCollection, isObject } from '@turf/helpers';
  import { collectionOf } from '@turf/invariant';
  import * as d3voronoi from 'd3-voronoi';
  
  /**
   * @param {Array<Array<number>>} coords representing a polygon
   * @returns {Feature<Polygon>} polygon
   */
  function coordsToPolygon(coords) {
      coords = coords.slice();
      coords.push(coords[0]);
      return polygon([coords]);
  }
  
  /**
   * Takes a FeatureCollection of points, and a bounding box, and returns a FeatureCollection
   * of Voronoi polygons.
   *
   * The Voronoi algorithim used comes from the d3-voronoi package.
   *
   * @name voronoi
   * @param {FeatureCollection<Point>} points to find the Voronoi polygons around.
   * @param {Object} [options={}] Optional parameters
   * @param {number[]} [options.bbox=[-180, -85, 180, -85]] clipping rectangle, in [minX, minY, maxX, MaxY] order.
   * @returns {FeatureCollection<Polygon>} a set of polygons, one per input point.
   * @example
   * var options = {
   *   bbox: [-70, 40, -60, 60]
   * };
   * var points = turf.randomPoint(100, options);
   * var voronoiPolygons = turf.voronoi(points, options);
   *
   * //addToMap
   * var addToMap = [voronoiPolygons, points];
   */
  function voronoi(points, options) {
      // Optional params
      options = options || {};
      if (!isObject(options)) throw new Error('options is invalid');
      var bbox = options.bbox || [-180, -85, 180, 85];
  
      // Input Validation
      if (!points) throw new Error('points is required');
      if (!Array.isArray(bbox)) throw new Error('bbox is invalid');
      collectionOf(points, 'Point', 'points');
  
      // Main
      return featureCollection(
          d3voronoi.voronoi()
              .x(function (feature) { return feature.geometry.coordinates[0]; })
              .y(function (feature) { return feature.geometry.coordinates[1]; })
              .extent([[bbox[0], bbox[1]], [bbox[2], bbox[3]]])
              .polygons(points.features)
              .map(coordsToPolygon)
      );
  }
  
  export default voronoi;
  
new_contents: import { polygon, featureCollection, isObject } from '@turf/helpers';
  import { collectionOf } from '@turf/invariant';
  import * as d3voronoi from 'd3-voronoi';
  
  /**
   * @private
   * @param {Array<Array<number>>} coords representing a polygon
   * @returns {Feature<Polygon>} polygon
   */
  function coordsToPolygon(coords) {
      coords = coords.slice();
      coords.push(coords[0]);
      return polygon([coords]);
  }
  
  /**
   * Takes a FeatureCollection of points, and a bounding box, and returns a FeatureCollection
   * of Voronoi polygons.
   *
   * The Voronoi algorithim used comes from the d3-voronoi package.
   *
   * @name voronoi
   * @param {FeatureCollection<Point>} points to find the Voronoi polygons around.
   * @param {Object} [options={}] Optional parameters
   * @param {number[]} [options.bbox=[-180, -85, 180, -85]] clipping rectangle, in [minX, minY, maxX, MaxY] order.
   * @returns {FeatureCollection<Polygon>} a set of polygons, one per input point.
   * @example
   * var options = {
   *   bbox: [-70, 40, -60, 60]
   * };
   * var points = turf.randomPoint(100, options);
   * var voronoiPolygons = turf.voronoi(points, options);
   *
   * //addToMap
   * var addToMap = [voronoiPolygons, points];
   */
  function voronoi(points, options) {
      // Optional params
      options = options || {};
      if (!isObject(options)) throw new Error('options is invalid');
      var bbox = options.bbox || [-180, -85, 180, 85];
  
      // Input Validation
      if (!points) throw new Error('points is required');
      if (!Array.isArray(bbox)) throw new Error('bbox is invalid');
      collectionOf(points, 'Point', 'points');
  
      // Main
      return featureCollection(
          d3voronoi.voronoi()
              .x(function (feature) { return feature.geometry.coordinates[0]; })
              .y(function (feature) { return feature.geometry.coordinates[1]; })
              .extent([[bbox[0], bbox[1]], [bbox[2], bbox[3]]])
              .polygons(points.features)
              .map(coordsToPolygon)
      );
  }
  
  export default voronoi;
  
subject: Update index.js