How to use the simple-statistics.mode function in simple-statistics

it('statistics methods on fields of array', () => {
    const data = [];
    for (let i = 1; i <= 10; i++) {
      // 1~10
      data.push({
        a: [i, i + 10, [-i, i * i, [-i * i, 1 / i]]],
      });
    }
    const dv = new DataSet.View().source(data);
    const values = flattenDeep(dv.getColumn('a'));
    expect(dv.max('a')).to.equal(max(values));
    expect(dv.min('a')).to.equal(min(values));
    expect(dv.mean('a')).to.equal(mean(values));
    expect(dv.average('a')).to.equal(mean(values));
    expect(dv.median('a')).to.equal(median(values));
    expect(dv.mode('a')).to.equal(mode(values));
    expect(dv.quantile('a', 0.5)).to.equal(quantile(values, 0.5));
    expect(dv.quantiles('a', [0, 0.1, 0.5])).to.eql(map([0, 0.1, 0.5], (p) => quantile(values, p)));
    expect(dv.quantilesByFraction('a', 4)).to.eql(map([0, 0.25, 0.5, 0.75, 1], (p) => quantile(values, p)));
    expect(dv.standardDeviation('a')).to.equal(standardDeviation(values));
    expect(dv.sum('a')).to.equal(sum(values));
    expect(dv.variance('a')).to.equal(variance(values));
    expect(dv.range('a')).to.eql([min(values), max(values)]);
  });
});

children.forEach(function(child) {
      key = child.join('/');
      if (key in tiles) {
        var tz = tiles[key];   // timezone name

        // Need to use timezone abbreviation becuase e.g. America/Los_Angeles
        // and America/Vancouver are the same. Use a time to determine the
        // abbreviation, in case two similar tz have slightly different
        // daylight savings schedule.
        var abbr = moment.tz(Date.now(), tz)._z.abbrs[0];
        votes.push(abbr);
        abbrs[abbr] = tz;
      }
    });

    if (votes.length > 1) return abbrs[ss.mode(votes)];
    else throw new Error('tile not found');
  }
}

it('statistics methods', () => {
    const dv = new DataSet.View().source(populationChina);
    dv.transform({
      type: 'map',
      callback(row) {
        row.year = parseInt(row.year, 10);
        return row;
      },
    });
    const years = dv.getColumn('year');
    expect(dv.max('year')).to.equal(max(years));
    expect(dv.min('year')).to.equal(min(years));
    expect(dv.mean('year')).to.equal(mean(years));
    expect(dv.average('year')).to.equal(mean(years));
    expect(dv.median('year')).to.equal(median(years));
    expect(dv.mode('year')).to.equal(mode(years));
    expect(dv.quantile('year', 0.5)).to.equal(quantile(years, 0.5));
    expect(dv.quantiles('year', [0, 0.1, 0.5])).to.eql(map([0, 0.1, 0.5], (p) => quantile(years, p)));
    expect(dv.quantilesByFraction('year', 4)).to.eql(map([0, 0.25, 0.5, 0.75, 1], (p) => quantile(years, p)));
    expect(dv.standardDeviation('year')).to.equal(standardDeviation(years));
    expect(dv.sum('year')).to.equal(sum(years));
    expect(dv.variance('year')).to.equal(variance(years));
    expect(dv.range('year')).to.eql([min(years), max(years)]);
  });

getToolset: function(chartType, headerlessCSV, headerIndex) {

      var columnArray = headerlessCSV.map(function(row) {
        return parseInt(row[headerIndex], 10);
      });

      var toolset = {
        Mean: Math.floor(stats.mean(columnArray)),
        Median: Math.floor(stats.median(columnArray)),
        Mode: Math.floor(stats.mode(columnArray)),
      };

      return toolset;
    }
  },