How to use the vt-pbf function in vt-pbf

if (!this._geoJSONIndex) {
        return callback(null, null);  // we couldn't load the file
    }

    const geoJSONTile = this._geoJSONIndex.getTile(canonical.z, canonical.x, canonical.y);
    if (!geoJSONTile) {
        return callback(null, null); // nothing in the given tile
    }

    const geojsonWrapper = new GeoJSONWrapper(geoJSONTile.features);

    // Encode the geojson-vt tile into binary vector tile form.  This
    // is a convenience that allows `FeatureIndex` to operate the same way
    // across `VectorTileSource` and `GeoJSONSource` data.
    let pbf = vtpbf(geojsonWrapper);
    if (pbf.byteOffset !== 0 || pbf.byteLength !== pbf.buffer.byteLength) {
        // Compatibility with node Buffer (https://github.com/mapbox/pbf/issues/35)
        pbf = new Uint8Array(pbf);
    }

    callback(null, {
        vectorTile: geojsonWrapper,
        rawData: pbf.buffer
    });
}