How to use @turf/flatten - 2 common examples

.reduce((memo, feature) => {
      if (feature.geometry.type === "MultiPolygon") {
        // Flatten any MultiPolygons to arrays of individual Polygon features,
        // because `booleanOverlap` can only compare like feature types.
        try {
          feature = flatten(feature).features;
        } catch (e) {
          // eslint-disable-next-line no-console
          console.error(e);
          Mixpanel.track("Error", {
            message: "unable to perform flatten on features",
            error: e,
          });

          feature = [];
        }
      }

      return memo.concat(feature);
    }, [])
    .filter(feature => {

getFeatures: GetFeatures = (type: 'LineString' | 'Point') =>
    turfFlatten(this.props.trackGeojson as any).features.filter(
      f => f && f.geometry && f.geometry.type === type,
    ) as any;