JavaScript Weird Part: Working with Date code samples

01-date.js

/**
 * today: Get the current date
 */
exports.today = () => new Date();
// main.js
const { today } = require("./date");
console.log(today()); // 2021-08-22T15:59:47.482Z

02-date.js

// date.js
/**
 * now: Get the current timestamp
 */
exports.now = () => Date.now();
// main.js
const { today, now } = require("./date");
console.log(now()); // 1629647987489

03-date.js

// date.js
const [HR, DAY, WEEK] = [
  60 * 60 * 1000,
  60 * 60 * 1000 * 24,
  60 * 60 * 1000 * 24 * 7,
];
exports.hourBefore = () => new Date(this.now() - HR);
exports.dayBefore = () => new Date(this.now() - DAY);
exports.weekBefore = () => new Date(this.now() - WEEK);
//main.js
console.log(hourBefore()); //2021-08-22T14:59:47.489Z
console.log(dayBefore()); // 2021-08-21T15:59:47.489Z
console.log(weekBefore()); // 2021-08-15T15:59:47.489Z

04-date.js

//date.js
const MONTHS = { 0: "January", 1: "February", 2: "March", 7: "August" }; // TODO: complete
exports.monthInString = (date) => {
  return MONTHS[date.getMonth()];
};
const DAYS = { 0: "Sunday", 1: "Monday", 2: "Tuesday", 3: "Wednesday" }; // TODO: complete
exports.dayOfWeek = (date) => {
  return DAYS[date.getDay()];
};
// main.js
console.log(monthInString(today())); // August
console.log(dayOfWeek(today())); // Monday

05-date.js

const [month, day, year, hr, min, sec, meridiem] = new Date(
  2021,
  08,
  22,
  18,
  08,
  08
)
  .toLocaleString("en-US")
  .split(/\W+/); 
////Output: 9/22/2021, 8:08:08 PM
console.log(month, day, year, hr, min, sec, meridiem); // 9 22 2021 6 08 08 PM

06-date.js

const [month, day, year, hr, min, sec] = new Date(2021, 08, 22, 18, 08, 08)
  .toLocaleString("en-US", {
    day: "2-digit",
    month: "long",
    year: "2-digit",
    hour: "2-digit",
    minute: "2-digit",
    second: "2-digit",
    hour12: false,
  })
  .split(/\W+/); //// 9/22/2021, 8:08:08 PM
console.log(month, day, year, hr, min, sec); 
// September 22 21 18 08 08

07-date.js

// Simple hacks working with the month(add/subtract):
// date.js
/**
 * addMonths: add a month to date
 * You can pass -(month) to subtract
 *
 * @param {Date} date
 * @param {number} months
 */
exports.addMonths = (date, months) => {
  var d = date.getDate();
  date.setMonth(date.getMonth() + +months);
  if (date.getDate() != d) {
    date.setDate(0);
  }
  return date;
};
exports.subMonths = (date, months) => this.addMonths(date, -1 * months);
//main.js
console.log(today(), addMonths(today(), 2)); //2021-08-22T16:30:11.826Z 2021-10-22T16:30:11.826Z
console.log(today(), subMonths(today(), 2)); //2021-08-22T16:34:10.895Z 2021-06-22T16:34:10.895Z

08-date.js

var date = new Date(Date.UTC(2012, 11, 20, 3, 0, 0));
// US English uses month-day-year order
console.log(new Intl.DateTimeFormat("en-US").format(date));
// → "12/19/2012"
// British English uses day-month-year order
console.log(new Intl.DateTimeFormat("en-GB").format(date));
// → "19/12/2012"
// Chinese
console.log(new Intl.DateTimeFormat("zh-TW").format(date));
// → "2012/12/20"

09-date.js

//date.js
exports.formatString = (format, date) => {
  const [MM, DD, YYYY, hh, mm, ss, A] = date
    .toLocaleString("en-US", {
      day: "2-digit",
      month: "2-digit",
      year: "numeric",
      hour: "2-digit",
      minute: "2-digit",
      second: "2-digit",
    })
    .split(/\W+/);
  const timeMap = { MM, DD, YYYY, hh, mm, ss, A };
  return format.replace(/(\w+)/g, (key) => timeMap[key]);
};
// main.js
var date = new Date(2012, 11, 20, 3, 0, 0);
console.log(formatString("DD-MM-YYYY hh:mm:ss A", date)); // 20-12-2012 03:00:00 AM

10-date.js

const users = [
  { name: "1", dob: "1989/8/26" },
  { name: "2", dob: "1989/8/23" },
  { name: "3", dob: "1989/8/25" },
];
const sortedUsers = users.sort(
  ({ dob: dob1 }, { dob: dob2 }) =>
    new Date(dob1).getTime() - new Date(dob2).getTime()
);
console.log(sortedUsers);
/**
[
  { name: '2', dob: '1989/8/23' },
  { name: '3', dob: '1989/8/25' },
  { name: '1', dob: '1989/8/26' }
]
**/

11-date.js

//date.js
exports.formatDuration = (ms) => {
  ms = Math.abs(ms);
  const time = {
    day: Math.floor(ms / 86400000),
    hour: Math.floor(ms / 3600000) % 24,
    minute: Math.floor(ms / 60000) % 60,
    second: Math.floor(ms / 1000) % 60,
    millisecond: Math.floor(ms) % 1000,
  };
  return Object.entries(time)
    .filter((val) => val[1] !== 0)
    .map(([key, val]) => `${val} ${key}${val !== 1 ? "s" : ""}`)
    .join(", ");
};
// main.js
console.log(formatDuration(34325055574));
// 397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds

12-date.js

const currentDate = today();
console.log(currentDate.toISOString()); // 2021-08-22T16:38:27.164Z
console.log(currentDate.getTime()); // 1629650307164
console.log(currentDate.getDate()); // 23
console.log(currentDate.getDay()); // 1
console.log(currentDate.getMonth()); // 7
console.log(currentDate.getFullYear()); // 2021
console.log(currentDate.getHours()); // 0
console.log(currentDate.getMinutes()); // 38

13-date.js

var options = {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric",
};
console.log(new Intl.DateTimeFormat("de-DE", options).format(date));
// → "Donnerstag, 20. Dezember 2012"

14-date.js

//date.js
exports.isValid = (date) => date.toString() !== "Invalid Date";
//main.js
console.log(isValid(new Date("2021-08-22T16:30:11.826Z"))); // true
console.log(isValid(new Date("ff-08-22T16:30:11.826Z"))); // false

15-date.js

//date.js
const isAfterDate = (dateA, dateB) => dateA > dateB;
const isBeforeDate = (dateA, dateB) => dateA < dateB;
//main.js
console.log(new Date(2021, 08, 11) > new Date(2021, 08, 10));
console.log(new Date(2021, 08, 09) > new Date(2021, 08, 10));
console.log(
  new Date(2021, 08, 10).toISOString() === new Date(2021, 08, 10).toISOString()
);