Replace let dataFrame with const dataframe

[pddpd]

// transform data into DataFrame
const generateDataFrame = () => {
  try {
    if (fields) {
      return new DataFrame(copyData, { columns: fields });
    } else {
      return new DataFrame(copyData);
    }
  } catch (error) {
    // if the input data cannot be transformed into DataFrame
    // eslint-disable-next-line no-console
    console.error("error: ", error);
    return [];
  }
};
const dataFrame: DataFrame = generateDataFrame();
if (!(dataFrame instanceof DataFrame)) return dataFrame;