How to use the turf.centroid function in turf

module.exports = function(data, tile, writeData, done) {
  var digiroadLayer = data.fonecta.fonecta;
  var diffLayer = data.osm.osm;
  var osmlint = 'digiroad';
  var resultDiffLayer = 0;
  var resultdDigiLayer = 0;

  var limits = {
    min_zoom: 12,
    max_zoom: 12
  };
  var bbox = turf.bbox(digiroadLayer);
  var bboxPolygon = turf.bboxPolygon(bbox);
  var centroidPt = turf.centroid(bboxPolygon);
  var tilePoly = cover.geojson(centroidPt.geometry, limits);
  var newtile = cover.tiles(centroidPt.geometry, limits);
  // digiroad
  for (var i = 0; i < diffLayer.features.length; i++) {
    var val = diffLayer.features[i];
    if (val.geometry.type == 'LineString') {
      var dist = turf.lineDistance(val, 'kilometers');
      resultDiffLayer = resultDiffLayer + dist;
    }
  }
  //digiroad layer
  for (var i = 0; i < digiroadLayer.features.length; i++) {
    var val = digiroadLayer.features[i];
    if (val.geometry.type == 'LineString') {
      var dist = turf.lineDistance(val, 'kilometers');
      resultdDigiLayer = resultdDigiLayer + dist;

diffFc.features = Object.keys(runkeeperPixels).map(function(hash){
    var tile = hash.split('/').map(parseFloat);
    var poly = turf.centroid(turf.polygon(tilebelt.tileToGeoJSON(tile).coordinates));
    poly.properties.count = runkeeperPixels[hash];
    return poly;
  });
  diffFc.features = diffFc.features.filter(function(cell){

dim.push(0.0);
                }
                demand.push(dim);
            }
            
            var landmark_polygons_of_interest = {"JFK Airport": 0, "LaGuardia Airport": 0, "Grand Central": 0, "Port Authority Bus Terminal": 0, "Penn Station": 0};
            var landmark_scalers = {"JFK Airport": 11000.0, "LaGuardia Airport": 9000.0, "Grand Central": 2000.0, "Port Authority Bus Terminal": 1000.0, "Penn Station": 2000.0};
            
            for (landmark_index = 0; landmark_index < landmarks_data["features"].length; landmark_index++) {
                var landmark = landmarks_data["features"][landmark_index];
                var landmark_name = landmark["properties"]["name"];
                if (landmark_name in landmark_polygons_of_interest) {
                    //console.log(landmark["geometry"]["coordinates"]);
                    var landmark_polygon = turf.polygon(landmark["geometry"]["coordinates"]);
                    landmark_polygons_of_interest[landmark_name] = landmark_polygon;
                    var landmark_centroid = turf.centroid(landmark_polygon);
                    console.log("Landmark "+landmark_name+" centroid in polygon: "+turf.inside(landmark_centroid, landmark_polygon));
                }
            }
            
            
            console.log("Calculating centroids");
            var centroids = [];
            for (tract_index = 0; tract_index < data.features.length; tract_index++) {
                var turf_centroid = turf.centroid(data.features[tract_index]);
                //var tract_area = turf.area(turf_polygons[tract_index]);
                centroids[tract_index] = turf_centroid;
            }
            
            console.log("Calculating voxels");
            for (i = 0; i < voxels_dim; i++) {
                var lat = lat_min + voxels_res_lat*i;

var atotal = aland + awater;
                                var scale_factor = 1.0 / (aland / atotal);
                                var population_scaled_for_land = record["POP10"] * scale_factor;
                                populations[record["GEOID"]] = population_scaled_for_land;
                                population_density[record["GEOID"]] = population_scaled_for_land/(record["ALAND"] * .0000003861);
                                if (population_scaled_for_land/(record["ALAND"] * .0000003861) > 1000.0) {
                                    dense_enough += 1;
                                }
                            }
                            console.log(dense_enough + " of " + population_records.length + " tracts are dense enough for consideration");

                            console.log("Calculating centroids");
                            var centroids = [];
                            var water_centroids = [];
                            for (tract_index = 0; tract_index < census_data.features.length; tract_index++) {
                                var turf_centroid = turf.centroid(turf_polygons[tract_index]);

                                //var tract_area = turf.area(turf_polygons[tract_index]);
                                centroids[tract_index] = turf_centroid;
                            }
                            for (var w = 0; w < water_data.features.length; w++) {
                                var water_centroid = turf.centroid(water_data.features[w]);
                                water_centroids[w] = water_centroid;
                            }


                            var dggrids_with_overlap = 0;
                            var dggrids_queried = 0;

                            for (var j = 0; j < dggrid_data.features.length; j++) {

                                var feature = dggrid_data.features[j];

var landmark = landmarks_data["features"][landmark_index];
                var landmark_name = landmark["properties"]["name"];
                if (landmark_name in landmark_polygons_of_interest) {
                    //console.log(landmark["geometry"]["coordinates"]);
                    var landmark_polygon = turf.polygon(landmark["geometry"]["coordinates"]);
                    landmark_polygons_of_interest[landmark_name] = landmark_polygon;
                    var landmark_centroid = turf.centroid(landmark_polygon);
                    console.log("Landmark "+landmark_name+" centroid in polygon: "+turf.inside(landmark_centroid, landmark_polygon));
                }
            }
            
            
            console.log("Calculating centroids");
            var centroids = [];
            for (tract_index = 0; tract_index < data.features.length; tract_index++) {
                var turf_centroid = turf.centroid(data.features[tract_index]);
                //var tract_area = turf.area(turf_polygons[tract_index]);
                centroids[tract_index] = turf_centroid;
            }
            
            console.log("Calculating voxels");
            for (i = 0; i < voxels_dim; i++) {
                var lat = lat_min + voxels_res_lat*i;
                for (j = 0; j < voxels_dim; j++) {
                    var lon = lon_min + voxels_res_lon*j;
                    var square = turf.bboxPolygon([lon, lat, lon+voxels_res_lon, lat+voxels_res_lat]);
                    var d = 0.0;
                    
                    for (tract_index = 0; tract_index < data.features.length; tract_index++) {
                        var tract = data.features[tract_index];
                        var ct2010 = tract.properties.TRACTCE10;
                        var centroid = centroids[tract_index];

hail.features = paths.features.map(function(path, k){
    var cent = turf.centroid(path);
    cent.properties.y = path.properties.YR;
    return cent;
});

var zoomedTiles = zoomedTiles.map(function(tile){
        var centroid =
          turf.centroid(
            turf.bboxPolygon(
              tilebelt.tileToBBOX(tile)
            )
          );
        return tilebelt.pointToTile(
          centroid.geometry.coordinates[0],
          centroid.geometry.coordinates[1], zoom);
      });
      return zoomedTiles;

var dggrids_queried = 0;

                            for (var j = 0; j < dggrid_data.features.length; j++) {

                                var feature = dggrid_data.features[j];

                                var dggrid_polygon = {
                                    "type": "Feature",
                                    "properties": {},
                                    "geometry": {
                                        "type": "Polygon",
                                        "coordinates": feature.geometry.coordinates
                                    }
                                };

                                var dggrid_centroid = turf.centroid(dggrid_polygon);

                                var wkt = 'POLYGON((';
                                for (var i = 0; i < feature["geometry"]["coordinates"][0].length; i++) {
                                    var coordinate = feature["geometry"]["coordinates"][0][i];
                                    wkt += coordinate[0];
                                    wkt += ' ';
                                    wkt += coordinate[1];
                                    if (i < feature["geometry"]["coordinates"][0].length - 1) {
                                        wkt += ', ';
                                    } else {
                                        wkt += '))';
                                    }
                                }

                                var has_overlap = false;
                                var all_water = false;

.pipe(through(function toEs(row) {

                var stream = this;

                if(irisMap.get(row.COM)) {

                    var center = turf.centroid(irisMap.get(row.COM));

                    var data = {
                        geometry: irisMap.get(row.COM).geometry,
                        center: center.geometry.coordinates
                    }

                    Object.keys(toKeep).map(label => {
                        data[toKeep[label]] = row[label];
                    })                    
                    
                    batch.push({index: {_index: 'iris', _type: 'iris'}});
                    batch.push(data)

                } 

                if (batch.length === 1000) {

data[1].features = data[1].features.filter(feature =>
        inside(centroid(feature), gapsCoverageExtent)
      ).forEach(feature => {