An example of reducing a set of data

Example.js

/*
Implement a function that given two arbitrary dates ‘dateFrom’ and ‘dateTo’, will display a sorted list of the stocks based on their performance over those dates. For example:
*/
const stocks = {
  AAPL: [
    {
      'date': '2016-03-02',
      'price': 98.32,
      'dayChange': -1.5
    },
    {
      'date': '2016-03-03',
      'price': 100.00,
      'dayChange': 2.60
    },
    {
      'date': '2016-03-04',
      'price': 101.2,
      'dayChange': -1.22
    },
    {
      'date': '2016-03-07',
      'price': 104.64,
      'dayChange': 3.44
    }
  ],
  FB: [
    {
      'date': '2016-03-02',
      'price': 98.32,
      'dayChange': -1.1
    },
    {
      'date': '2016-03-03',
      'price': 100.00,
      'dayChange': 1.68
    },
    {
      'date': '2016-03-04',
      'price': 101.2,
      'dayChange': 1.2
    },
    {
      'date': '2016-03-07',
      'price': 104.64,
      'dayChange': 3.44
    }
  ],
  GOOGL: [
    {
      'date': '2016-03-02',
      'price': 98.32,
      'dayChange': -1.1
    },
    {
      'date': '2016-03-03',
      'price': 100.00,
      'dayChange': 1.68
    },
    {
      'date': '2016-03-04',
      'price': 101.2,
      'dayChange': -12
    },
    {
      'date': '2016-03-07',
      'price': 104.64,
      'dayChange': 1.44
    }
  ]
};

const _ = require('underscore');
const showPerformanceBetweenDates2 = (startDate, endDate) => {
  const start = new Date(startDate).getTime();
  const end = new Date(endDate).getTime();
  const now = new Date().getTime()

  if (start > end) { return console.log('Dates are out of order'); }
  if (now - start > 31536000000) { return console.log('Start date is over 1 year old'); }

  _.mapObject(stocks, (value, key) => {
    stocks[key] = value.filter((s) => {
      const thisDate = new Date(s.date).getTime();
      return thisDate >= start && thisDate <= end;
    })
    .reduce((totalValue, currentDay) => (totalValue + currentDay.dayChange), 0);
  });

  console.log(stocks);
};

showPerformanceBetweenDates2('2016-03-03', '2016-03-04')