timezone-shift

🚀 Live Demo

Lightweight, dependency-free timezone utility with multi-timezone DST support for TypeScript/JavaScript.

Features

• 🌍 Multi-timezone support: Europe/London, America/New_York, America/Los_Angeles, Europe/Paris, Europe/Berlin, Asia/Tokyo, Australia/Sydney
• 🕒 Accurate DST handling: Uses platform timezone databases for always-current DST rules
• 🪶 Lightweight: Zero external dependencies, minimal footprint
• 🔧 Type-safe: Complete TypeScript definitions
• 🌐 Cross-platform: Works in Node.js and browsers
• 🧪 Well-tested: 162+ tests including DST edge cases

Installation

npm install timezone-shift

Quick Start

import { isDST, toTimezoneParts, dstTransitionDates } from "timezone-shift";

// Check if London is in DST
const londonDST = isDST(new Date(), "Europe/London");

// Get timezone parts
const parts = toTimezoneParts(new Date(), "America/New_York");

// Get DST transitions for the year
const transitions = dstTransitionDates(2025, "Europe/London");

Working Hours & Business Logic

import {
  inWorkingHours,
  isWorkingDay,
  inWorkingHoursLondon,
} from "timezone-shift";

const meetingTime = new Date("2024-07-15T14:30:00Z");

// Default working hours: 9:00-17:30 local time
console.log(inWorkingHours(meetingTime, "Europe/London")); // true
console.log(inWorkingHours(meetingTime, "America/New_York")); // true (10:30 EDT)

// Check if it's a working day (Monday-Friday)
console.log(isWorkingDay(meetingTime)); // true (if Monday-Friday)

// London-specific convenience function
console.log(inWorkingHoursLondon(meetingTime)); // true

Handling DST Transitions

import { dstTransitionDates, isDST } from "timezone-shift";

// Get DST boundaries for a year
const ukTransitions = dstTransitionDates(2024, "Europe/London");
console.log(ukTransitions?.dstStartUtc); // 2024-03-31T01:00:00.000Z (BST starts)
console.log(ukTransitions?.dstEndUtc); // 2024-10-27T01:00:00.000Z (GMT resumes)

// Test dates around transitions
const beforeDST = new Date("2024-03-30T12:00:00Z");
const afterDST = new Date("2024-04-01T12:00:00Z");

console.log(isDST(beforeDST, "Europe/London")); // false (GMT)
console.log(isDST(afterDST, "Europe/London")); // true (BST)

Development

Clone the repository and install dependencies:

git clone https://github.com/martin-nolan/timezone-shift.git
cd timezone-shift
npm install

Run tests:

npm test

License

MIT - see LICENSE file.

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Need more examples? Check out the Release Notes for detailed documentation and use cases.