Date and Time

const nowUnix = Date.now() // milliseconds since the epoch
console.log(nowUnix)
 
const datestr = '2019-01-17T09:24:23+00:00'
const date = new Date(datestr)
console.log(date.getTime()) // milliseconds
console.log(date.toString()) // in the machine's local timezone
 
const futureDate = new Date(date)
futureDate.setDate(date.getDate() + 14) // mutates in place
console.log(futureDate.toString())
 
const formatted = new Intl.DateTimeFormat('en-US', {
  year: 'numeric',
  month: '2-digit',
  day: '2-digit',
}).format(date)
console.log(formatted) // 01/17/2019

package main
 
import (
	"fmt"
	"time"
)
 
func main() {
	nowUnix := time.Now().Unix() // seconds since the epoch
	fmt.Println(nowUnix)
 
	datestr := "2019-01-17T09:24:23+00:00"
	date, err := time.Parse(time.RFC3339, datestr)
	if err != nil {
		panic(err)
	}
 
	fmt.Println(date.Unix())
	fmt.Println(date.String())
 
	futureDate := date.AddDate(0, 0, 14) // returns a new time.Time, doesn't mutate `date`
	fmt.Println(futureDate.String())
 
	// time.DateOnly is the predefined "2006-01-02" layout
	fmt.Println(futureDate.Format(time.DateOnly))
 
	formatted := date.Format("01/02/2006") // layout based on the reference date, not tokens
	fmt.Println(formatted)
}

// Cargo.toml: chrono = "0.4"
use std::time::{SystemTime, UNIX_EPOCH};
 
use chrono::{DateTime, Duration};
 
fn main() {
    let now_unix = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap()
        .as_secs(); // seconds since the epoch
    println!("{now_unix}");
 
    let datestr = "2019-01-17T09:24:23+00:00";
    let date = DateTime::parse_from_rfc3339(datestr).unwrap();
    println!("{}", date.timestamp());
    println!("{date}");
 
    let future_date = date + Duration::days(14); // returns a new DateTime, doesn't mutate `date`
    println!("{future_date}");
 
    let formatted = date.format("%m/%d/%Y"); // strftime-style specifiers, not a reference date
    println!("{formatted}");
}

import Foundation
 
let nowUnix = Int(Date.now.timeIntervalSince1970) // seconds since the epoch
print(nowUnix)
 
let datestr = "2019-01-17T09:24:23+00:00"
let date = try Date(datestr, strategy: .iso8601)
print(Int(date.timeIntervalSince1970))
print(date)
 
// returns a new Date, doesn't mutate `date`
let futureDate = Calendar.current.date(byAdding: .day, value: 14, to: date)!
print(futureDate)
 
let formatted = date.formatted(.dateTime.year().month(.twoDigits).day(.twoDigits).locale(Locale(identifier: "en_US")))
print(formatted)

void main() {
    long nowUnix = Instant.now().getEpochSecond(); // seconds since the epoch; OffsetDateTime/Instant/DateTimeFormatter are all in java.base, auto-imported
    IO.println(nowUnix);
 
    String datestr = "2019-01-17T09:24:23+00:00";
    OffsetDateTime date = OffsetDateTime.parse(datestr);
    IO.println(date.toEpochSecond());
    IO.println(date);
 
    OffsetDateTime futureDate = date.plusDays(14); // returns a new OffsetDateTime, doesn't mutate `date`
    IO.println(futureDate);
 
    String formatted = date.format(DateTimeFormatter.ofPattern("MM/dd/yyyy"));
    IO.println(formatted);
}