getDisplayTime.js

function getDaysInMonth(month, year) {
  return new Date(year, month, 0).getDate();
}

function getIntervals(year) {
  const months = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
  let min = 0;
  let max = 0;

  return months.map(month => {
    min = max + 1;
    max = max + getDaysInMonth(month, year);

    return {
      month,
      min,
      max,
    };
  });
}

export default function getDisplayTime(date1, date2) {
  const date1MS = date1.getTime();
  const date2MS = date2.getTime();

  // Calculate the difference in milliseconds
  let differenceMS = date2MS - date1MS;

  differenceMS = differenceMS / 1000;
  const seconds = Math.floor(differenceMS % 60);
  differenceMS = differenceMS / 60;
  const minutes = Math.floor(differenceMS % 60);
  differenceMS = differenceMS / 60;
  const hours = Math.floor(differenceMS % 24);
  const days = Math.floor(differenceMS / 24);
  let display = undefined;

  if (days > 0) {
    const date2Year = date2.getFullYear();
    const intervals = getIntervals(date2Year);
    for (let i = 0; i < intervals.length; i++) {
      const { month, min, max } = intervals[i];
      if (days === max) {
        display = `${month} tháng trước`;
      }

      if (days >= min && days < max) {
        display = `${days} ngày trước`;
      }
    }
  } else {
    const times = [
      { value: hours, suffix: 'giờ trước' },
      { value: minutes, suffix: 'phút trước' },
      { value: seconds, suffix: 'giây trước' },
    ];

    for (let i = 0; i < times.length; i++) {
      if (times[i].value > 0) {
        display = `${times[i].value} ${times[i].suffix}`;
        break;
      }
    }
  }

  if (!display) {
    let date = date1.getDate();
    let month = date1.getMonth() + 1;
    const year = date1.getFullYear();

    date = date < 10 ? `0${date}` : date;
    month = month < 10 ? `0${month}` : month;

    display = `${date}-${month}-${year}`;
  }

  return {
    display,
    seconds,
    minutes,
    hours,
    days,
  };
}

getDisplayTime.test.js

import getDisplayTime from '../src/getDisplayTime';

// 14-01-2019 17:02:26
const nowValue = 1547460146038;

test('2 phút trước', () => {
  const adTime = new Date(1547460024000);
  const now = new Date(nowValue);
  const { display, days, hours, minutes, seconds } = getDisplayTime(
    adTime,
    now,
  );
  expect(display).toBe('2 phút trước');
  expect(days).toBe(0);
  expect(hours).toBe(0);
  expect(minutes).toBe(2);
  expect(seconds).toBe(2);
});

test('9 giờ trước', () => {
  const adTime = new Date(1547425290000);
  const now = new Date(nowValue);
  const { display, days, hours, minutes, seconds } = getDisplayTime(
    adTime,
    now,
  );
  expect(display).toBe('9 giờ trước');
  expect(days).toBe(0);
  expect(hours).toBe(9);
  expect(minutes).toBe(40);
  expect(seconds).toBe(56);
});

test('18 ngày trước', () => {
  const adTime = new Date(1545897844000);
  const now = new Date(nowValue);
  const { display, days, hours, minutes, seconds } = getDisplayTime(
    adTime,
    now,
  );
  expect(display).toBe('18 ngày trước');
  expect(days).toBe(18);
  expect(hours).toBe(1);
  expect(minutes).toBe(58);
  expect(seconds).toBe(22);
});

test('01-02-2017', () => {
  const adTime = new Date(1485882000000);
  const now = new Date(nowValue);
  const { display, days, hours, minutes, seconds } = getDisplayTime(
    adTime,
    now,
  );
  expect(display).toBe('01-02-2017');
  expect(days).toBe(712);
  expect(hours).toBe(17);
  expect(minutes).toBe(2);
  expect(seconds).toBe(26);
});

test('2 tháng trước', () => {
  const adTime = new Date(1542301200000);
  const now = new Date(nowValue);
  const { display, days, hours, minutes, seconds } = getDisplayTime(
    adTime,
    now,
  );
  expect(display).toBe('2 tháng trước');
  expect(days).toBe(59);
  expect(hours).toBe(17);
  expect(minutes).toBe(2);
  expect(seconds).toBe(26);
});