code: function negativeValues(series) {
    let i, j, data;
    for (i = 0; i < series.length; i++) {
      data = series[i].data;
      for (j = 0; j < data.length; j++) {
        if (data[j][1] < 0) {
          return true;
        }
      }
    }
    return false;
  }
docs: end iso8601.js