calculateDateText.js

import React from 'react';
import moment from 'moment';
import {
  FormattedDate,
  FormattedMessage
} from 'react-intl';

export default function calculateDateText(fromDate, now, toDate) {
  let text;
  // toDate and fromDate aren't in the same year OR
  // toDate is not in current year, then show year.
  const sameYearMessages = toDate.diff(fromDate, 'years') === 0;
  const sameYearNow = toDate.diff(now, 'years') === 0;

  if (!sameYearMessages || !sameYearNow) {
    text = (
      <FormattedDate
        day="numeric"
        month="long"
        value={toDate.toDate()}
        year="numeric"
      />
    );
  }
  // from.day < to.day assume from.day < now.day. must check to.day == now.day
  else if (now.diff(toDate, 'days') === 0) {
    text = (
      <FormattedMessage
        defaultMessage="Today"
        description="Day indicator for the current day"
        id="ciscospark.datetime.today"
      />
    );
  }
  // from.day < to.day < now.day therefore from cannot be yesterday
  // only need to check to.day == now.day - 1
  else if (moment(now).subtract(1, 'days').diff(toDate, 'days') === 0) {
    text = (
      <FormattedMessage
        defaultMessage="Yesterday"
        description="Day indicator for the previous day"
        id="ciscospark.datetime.yesterday"
      />
    );
  }
  else {
    // older than yesterday.
    text = (
      <FormattedDate
        day="numeric"
        month="long"
        value={toDate.toDate()}
      />
    );
  }

  return text;
}