async function plotROC(fprs, tprs, epoch) {
  epoch++;  // Convert zero-based to one-based.

  // Store the series name in the list of series
  const seriesName = 'epoch ' +
      (epoch < 10 ? `00${epoch}` : (epoch < 100 ? `0${epoch}` : `${epoch}`))
  rocSeries.push(seriesName);

  const newSeries = [];
  for (let i = 0; i < fprs.length; i++) {
    newSeries.push({
      x: fprs[i],
      y: tprs[i],
    });
  }
  rocValues.push(newSeries);

  return tfvis.render.linechart(
      document.getElementById('rocCurve'),
      {values: rocValues, series: rocSeries},
      {
        width: 450,
        height: 320,
      },
  );
}
Plot a ROC curve.
@param {number[]} fprs False positive rates.
@param {number[]} tprs True positive rates, must have the same length as
  `fprs`.
@param {number} epoch Epoch number.