How to use the @mapbox/mapbox-gl-style-spec.format function in @mapbox/mapbox-gl-style-spec

downloadStyle() {
    const tokenStyle = format(stripAccessTokens(style.replaceAccessTokens(this.props.mapStyle)));

    const blob = new Blob([tokenStyle], {type: "application/json;charset=utf-8"});
    let exportName;
    if(this.props.mapStyle.name) {
      exportName = Slugify(this.props.mapStyle.name, '_')
    } else {
      exportName = this.props.mapStyle.id
    }
    saveAs(blob, exportName + ".json");
  }