Javascript での日付の操作: new Date() vs Day.js vs Moment.js

const now = new Date(); // Current date and time
const specificDate = new Date('2024-07-16'); // Specific date

const now = new Date();
const year = now.getFullYear();
const month = now.getMonth() + 1; // Months are zero-indexed
const day = now.getDate();

const hours = now.getHours();
const minutes = now.getMinutes();
const seconds = now.getSeconds();

const now = new Date();

now.setFullYear(2025);
now.setMonth(11); // December
now.setDate(25);

now.setHours(10);
now.setMinutes(11);
now.setSeconds(12);

const tomorrow = new Date();
tomorrow.setDate(tomorrow.getDate() + 1);

const now = new Date();
const dateString = now.toDateString(); // Example: 'Tue Jul 16 2024'
const timeString = now.toTimeString(); // Example: '14:12:34 GMT+0200 (Central European Summer Time)'

const parsedDate = new Date(Date.parse('2024-07-16T14:12:34Z'));

const date1 = new Date('2024-07-16');
const date2 = new Date('2024-07-17');
const isSame = date1.getTime() === date2.getTime(); // false
const isBefore = date1.getTime() < date2.getTime(); // true

const dayOfWeek = now.getDay(); // 0 for Sunday, 1 for Monday, etc.

const now = new Date();
const isoDate = now.toISOString(); // 2024-07-22T11:30:59.827Z
const utcDate = now.toUTCString(); // Mon, 22 Jul 2024 11:30:42 GMT

const date1 = new Date('2024-01-01');
const date2 = new Date('2024-12-31');
const differenceInTime = date2 - date1;
const differenceInDays = differenceInTime / (1000 * 3600 * 24);
console.log(differenceInDays);

// Day.js
const Day.jsDate = Day.js().format('YYYY-MM-DD HH:mm:ss');

// Moment.js
const momentDate = moment().format('YYYY-MM-DD HH:mm:ss');

// Day.js
Day.js.extend(relativeTime); // require RelativeTime plugin
Day.js('2024-01-01').from(Day.js('2023-01-01')); // a year ago

// Moment.js
moment('2024-01-01').from(moment('2023-01-01')); // a year ago

Day.js.extend(utc);
Day.js.extend(timezone);
Day.js('2024-07-16 14:12:34').tz('America/New_York');

// Moment.js with moment-timezone
moment.tz('2024-07-16 14:12:34', 'America/New_York');

// Day.js
Day.js.locale('fr');
const frenchDate = Day.js().format('LLLL'); // dimanche 15 juillet 2012 11:01

// Moment.js
moment.locale('fr');
const frenchMomentDate = moment().format('LLLL'); // dimanche 15 juillet 2012 11:01

// Day.js
const invalidDay.js = Day.js('invalid date');
if (!invalidDay.js.isValid()) {
    console.log('Invalid date');
}

// Moment.js
const invalidMoment = moment('invalid date');
if (!invalidMoment.isValid()) {
    console.log('Invalid date');
}

// Day.js with customParseFormat plugin
Day.js.extend(customParseFormat);
const complexDate = Day.js('05/02/69 1:02:03 PM -05:00', 'MM/DD/YY H:mm:ss A Z');

// Moment.js
const complexMoment = moment('05/02/69 1:02:03 PM -05:00', 'MM/DD/YY H:mm:ss A Z');

// Day.js
Day.js.extend(duration);
const durationDay.js = Day.js.duration(5000); // 5 seconds
console.log(durationDay.js.asMinutes()); // 0.083333...
const humanizedDurationDay.js = Day.js.duration(5000).humanize(); // 'a few seconds'

// Moment.js
const durationMoment = moment.duration(5000); // 5 seconds
console.log(durationMoment.asMinutes()); // 0.083333...
const humanizedDurationMoment = moment.duration(5000).humanize(); // 'a few seconds'