タイムゾーン変換

// Convert a date from one timezone to another
const date = new Date('2026-03-15T09:00:00Z')

// Format in specific timezone
const nyTime = date.toLocaleString('en-US', { timeZone: 'America/New_York' })
// → "3/15/2026, 5:00:00 AM"

const tokyoTime = date.toLocaleString('en-US', { timeZone: 'Asia/Tokyo' })
// → "3/15/2026, 6:00:00 PM"

// Get the UTC offset for a timezone programmatically
function getUtcOffset(tz: string, date = new Date()) {
  const fmt = new Intl.DateTimeFormat('en-US', {
    timeZone: tz,
    timeZoneName: 'longOffset',
  })
  const parts = fmt.formatToParts(date)
  return parts.find(p => p.type === 'timeZoneName')?.value ?? ''
}
getUtcOffset('Asia/Kolkata') // → "GMT+05:30"

from datetime import datetime
from zoneinfo import ZoneInfo

# Create a timezone-aware datetime
dt = datetime(2026, 3, 15, 9, 0, tzinfo=ZoneInfo('UTC'))

# Convert to New York time
ny = dt.astimezone(ZoneInfo('America/New_York'))
print(ny)  # → 2026-03-15 05:00:00-04:00 (EDT in March)

# Convert to Tokyo time
tokyo = dt.astimezone(ZoneInfo('Asia/Tokyo'))
print(tokyo)  # → 2026-03-15 18:00:00+09:00

# Get current time in any timezone
now_berlin = datetime.now(ZoneInfo('Europe/Berlin'))
print(now_berlin.strftime('%Y-%m-%d %H:%M %Z'))  # → 2026-03-15 10:00 CET

package main

import (
	"fmt"
	"time"
)

func main() {
	utc := time.Date(2026, 3, 15, 9, 0, 0, 0, time.UTC)

	// Load timezone by IANA name
	ny, _ := time.LoadLocation("America/New_York")
	tokyo, _ := time.LoadLocation("Asia/Tokyo")

	fmt.Println(utc.In(ny))    // → 2026-03-15 05:00:00 -0400 EDT
	fmt.Println(utc.In(tokyo)) // → 2026-03-15 18:00:00 +0900 JST

	// Get the UTC offset in seconds
	_, offset := utc.In(ny).Zone()
	fmt.Printf("UTC offset: %+d hours\n", offset/3600) // → UTC offset: -4 hours
}

# Display current time in a specific timezone
TZ='Asia/Tokyo' date '+%Y-%m-%d %H:%M:%S %Z'
# → 2026-03-15 18:00:00 JST

# Convert a UTC timestamp to another timezone
TZ='America/Los_Angeles' date -d '2026-03-15T09:00:00Z' '+%Y-%m-%d %H:%M %Z'
# → 2026-03-15 02:00 PDT

# List all available IANA timezone names
timedatectl list-timezones | head -20