kk-date - Advanced JavaScript Date Library

A blazing-fast JavaScript date library with intelligent caching, automatic DST detection, and zero-config timezone handling. Perfect for high-performance applications, real-time systems, and data-intensive operations where speed and accuracy matter most.

🌟 Why Choose kk-date?

Performance & Efficiency (measured on Node.js 26; reproduced by CI, results vary)

⚡ Lightning Fast - Over 50x faster timezone operations than Day.js
🚀 ~95% Faster Overall - Fastest in every scenario vs Moment.js, Day.js, and Luxon
💾 Memory Efficient - Object pooling + LRU cache eviction keep long-running processes stable
⚙️ Smart Caching - ~32% faster repeated operations with built-in caching

Reliability & Safety

🛡️ Fail-Fast Design - Invalid dates immediately throw errors, preventing silent bugs in production
🎯 Type Safety - Rejects malformed dates instead of returning unexpected results
✅ Predictable Behavior - Never continues with invalid dates, unlike libraries that return "Invalid Date"
🔒 Production Tested - 585 comprehensive tests covering edge cases and DST transitions

Features & Compatibility

🌍 Accurate Timezone Handling - Fast, DST-aware timezone conversions with perfect accuracy
🧠 Zero-Config DST - Automatic Daylight Saving Time detection without manual intervention
📊 Big Data Ready - Handles 1M-operation workloads efficiently
🌍 Production Proven - Cross-platform compatibility with zero dependencies

📦 Installation

npm install kk-date

🚨 Breaking Changes in v5.0.0

format_c() was removed. Dynamic format() templates cover every use case in a single call:

// before (v4): date.format_c(' ', 'DD', 'MMMM', 'YYYY')
date.format('DD MMMM YYYY');

// separators that could read as tokens go in [brackets]:
// before (v4): date.format_c('T', 'YYYY-MM-DD', 'HH:mm:ss')
date.format('YYYY-MM-DDTHH:mm:ss');

format() now supports the full moment/dayjs display-token vocabulary — YY M Mo Q Qo DDD DDDo DDDD d dd do e E w wo ww W Wo WW gg gggg GG GGGG H h k kk m s S..SSSSSSSSS Z ZZ z zz zzz plus in-template X/x were added to the existing 16 tokens. Because many single letters are now significant, unbracketed literal words in templates can change output — bracket literal text ('[Week] w'), exactly as in moment/dayjs. See the supported tokens table.

See the migration guide for details.

🚀 Quick Start

const kk_date = require('kk-date');

// Enable caching for high-performance applications
kk_date.caching({ status: true, defaultTtl: 3600 });

// Create and format dates
const date = new kk_date('2024-08-23 10:30:00');
console.log(date.format('YYYY-MM-DD HH:mm:ss')); // 2024-08-23 10:30:00

// Format templates are dynamic: combine the supported tokens any way you like.
// Templates are compiled once and cached, so custom combinations stay fast.
console.log(date.format('YYYYMM'));              // 202408
console.log(date.format('HHmm'));                // 1030
console.log(date.format('[Created:] DD MMMM')); // Created: 23 August

// Safe error handling - catches invalid dates early!
try {
    const invalid = new kk_date('invalid-date'); // ❌ Throws error immediately
} catch (error) {
    console.log('Invalid date prevented!'); // ✅ Error caught, no silent bugs
}

// Pre-validate dates without throwing errors (the static isValid() requires a format template)
if (kk_date.isValid('2024-13-45', 'YYYY-MM-DD')) { // false - invalid month
    // Won't execute
}
if (kk_date.isValid('2024-08-23', 'YYYY-MM-DD')) { // true - valid date
    const safeDate = new kk_date('2024-08-23'); // ✅ Safe to create
}

// isValid accepts ANY display-token template, not just the predefined ones
kk_date.isValid('31/12/2024 23:59', 'DD/MM/YYYY HH:mm'); // true
kk_date.isValid('03:45', 'mm:ss');                       // true - minutes:seconds

// Optional strict mode (moment strict parity): real calendar days + wall-clock hours
kk_date.isValid('2021-02-30', 'YYYY-MM-DD');       // true  - shape check only (default)
kk_date.isValid('2021-02-30', 'YYYY-MM-DD', true); // false - Feb 30 doesn't exist
kk_date.isValid('25:00:00', 'HH:mm:ss');           // true  - day-overflow support (default)
kk_date.isValid('25:00:00', 'HH:mm:ss', true);     // false - strict wall-clock hours
// Migrating from moment(value, format, true).isValid()? Pass true as the 3rd argument.

// Zero-config timezone conversion with automatic DST detection.
// Note: a naive string like '2024-08-23 10:30:00' is parsed in the process's LOCAL timezone.
// The examples below assume the process timezone is UTC (run with TZ=UTC, or call
// kk_date.setTimezone('UTC')). Pass an absolute instant ('...Z') for identical results everywhere.
const nyTime = new kk_date('2024-08-23 10:30:00').tz('America/New_York');
console.log(nyTime.format('HH:mm')); // 06:30 (EDT - automatically detected)

const tokyoTime = new kk_date('2024-08-23 10:30:00').tz('Asia/Tokyo');
console.log(tokyoTime.format('HH:mm')); // 19:30 (JST)

// Lightning-fast date manipulation
const tomorrow = new kk_date('2024-08-23 10:30:00').add(1, 'days');
console.log(tomorrow.format('YYYY-MM-DD')); // 2024-08-24

📚 Documentation

📖 Complete API Reference

Comprehensive documentation of all available methods and properties.

🕐 Timezone Guide

Detailed guide on timezone handling, DST support, and conversion examples.

📅 Formatting Guide

Complete list of supported date/time formats with examples.

⚙️ Configuration Guide

How to configure global settings, locales, and timezone preferences.

⚡ Performance Guide

Comprehensive benchmarks, optimization strategies, and performance monitoring.

🔧 Advanced Usage

Advanced features, performance tips, and best practices.

🧪 Testing Guide

How to run tests and contribute to the project.

🌍 Timezone Accuracy & Reliability

Why Timezone Accuracy Matters

Timezone handling is one of the most critical aspects of date libraries. Inconsistent timezone conversions can lead to:

Data corruption in financial applications
Scheduling conflicts in calendar systems
User confusion in global applications
Production bugs that are hard to detect

kk-date vs Other Libraries

Library	Timezone Accuracy	DST Handling	Cross-Platform Consistency	Configuration Required
kk-date	✅ Perfect	✅ Automatic	✅ Consistent	✅ Zero Config
Moment.js	⚠️ System Dependent	⚠️ Manual Setup	❌ Inconsistent	⚠️ Complex Setup
Day.js	⚠️ System Dependent	⚠️ Plugin Required	❌ Inconsistent	⚠️ Plugin Setup

Real-World Example

// Test instant: an absolute UTC instant (ISO-8601 with 'Z') is unambiguous on every machine.
// (A naive string like '2024-08-23 10:00:00' would instead be parsed in the process's local
// timezone, so pass an absolute instant when you need identical results everywhere.)
const testDate = '2024-08-23T10:00:00.000Z';

// kk-date: absolute instant converts to the same wall-clock on every system
const kkDate = new kk_date(testDate).tz('America/New_York');
console.log(kkDate.format('YYYY-MM-DD HH:mm:ss'));
// Result: 2024-08-23 06:00:00 (identical on every system)

// Moment.js: requires the moment-timezone add-on for .tz()
const moment = require('moment-timezone');
const momentDate = moment(testDate);
console.log(momentDate.tz('America/New_York').format('YYYY-MM-DD HH:mm:ss'));
// Result: 2024-08-23 06:00:00 (needs moment-timezone)

// Day.js: requires the utc + timezone plugins for .tz()
const dayjs = require('dayjs');
const dayjsDate = dayjs(testDate);
console.log(dayjsDate.tz('America/New_York').format('YYYY-MM-DD HH:mm:ss'));
// Result: 2024-08-23 06:00:00 (needs dayjs timezone plugin)

Cross-Platform Consistency

kk-date provides identical results across different systems:

// Same code, same results on Windows, macOS, Linux, and Docker.
// Use an absolute instant (ISO-8601 with 'Z') so the value does not depend on the system timezone.
const baseTime = '2024-08-23T10:00:00.000Z';

// These results are identical on all platforms:
console.log(new kk_date(baseTime).tz('UTC').format('YYYY-MM-DD HH:mm:ss'));        // 2024-08-23 10:00:00
console.log(new kk_date(baseTime).tz('America/New_York').format('YYYY-MM-DD HH:mm:ss')); // 2024-08-23 06:00:00
console.log(new kk_date(baseTime).tz('Europe/London').format('YYYY-MM-DD HH:mm:ss'));    // 2024-08-23 11:00:00
console.log(new kk_date(baseTime).tz('Asia/Tokyo').format('YYYY-MM-DD HH:mm:ss'));       // 2024-08-23 19:00:00

Automatic DST Detection

kk-date automatically handles Daylight Saving Time transitions:

// DST transition dates - kk-date handles automatically.
// (Naive inputs below assume the process timezone is UTC; see the note above.)
const dstStart = new kk_date('2024-03-10 02:30:00'); // near DST start
const dstEnd = new kk_date('2024-11-03 02:30:00');   // near DST end

console.log(new kk_date('2024-03-10 02:30:00').tz('America/New_York').format('YYYY-MM-DD HH:mm:ss'));
// Result: 2024-03-09 21:30:00 (EST, correctly adjusted)

console.log(new kk_date('2024-11-03 02:30:00').tz('America/New_York').format('YYYY-MM-DD HH:mm:ss'));
// Result: 2024-11-02 22:30:00 (EDT, correctly adjusted)

Safety Comparison: kk-date vs Others

// ❌ Moment.js & Day.js - Silent failures can cause production bugs
const momentDate = moment('invalid-date');
console.log(momentDate.isValid()); // false
console.log(momentDate.format('YYYY-MM-DD')); // 'Invalid date' - but continues!
// Risk: This string can propagate through your app causing unexpected behavior

// ✅ kk-date - Fail-fast approach prevents bugs
try {
    const kkDate = new kk_date('invalid-date'); // Throws immediately!
} catch (error) {
    // Handle error properly - no silent failures
    console.log('Date validation failed - handling error safely');
}

Why Other Libraries Fail

Moment.js and Day.js have fundamental issues:

System Timezone Dependency: Results vary based on the server's timezone
Manual DST Configuration: Requires complex setup for DST handling
Plugin Requirements: Need additional plugins for timezone support
Inconsistent Results: Same code produces different results on different systems

kk-date solves these problems with:

Built-in timezone support (no plugins needed)
Automatic DST detection (no manual configuration)
Cross-platform consistency (same results everywhere)
Zero configuration (works out of the box)

🎯 Performance & Reliability

🚀 Intelligent Caching System (~70% Performance Boost)

// Enable high-performance caching for massive speed improvements
kk_date.caching({ status: true, defaultTtl: 3600 });

// Caching speeds up REPEATED operations (the same input parsed/formatted/converted again).
// Measured aggregate: ~70% faster on repeated operations, ~100% cache hit ratio for repeated inputs.
// (Distinct-input / first-time operations are already fast without caching.)

// Monitor cache performance
const stats = kk_date.caching_status();
const hitRate = stats.totalHits > 0 ? (stats.totalHits / (stats.totalHits + stats.total) * 100).toFixed(1) : 0;
console.log('Cache hit rate:', hitRate + '%'); // Typically 99%+
console.log('Cache size:', stats.cacheSize + '/' + stats.maxCacheSize); // Current/Max
console.log('Performance gain:', '~70%'); // Representative measured improvement (varies)

// Handle millions of operations efficiently
for (let i = 0; i < 1000000; i++) {
    const date = new kk_date('2024-08-23 10:00:00');
    date.tz('America/New_York'); // Much faster on repeat (served from cache)
}

When to Enable Caching:

📊 Data processing pipelines with repeated date operations
🌍 Global applications with multiple timezone conversions
⚡ Real-time systems requiring low-latency date operations
📈 Analytics dashboards with thousands of date calculations
🔄 APIs serving high-frequency date/time requests

Zero-Config DST Handling

// Automatic DST detection - no manual configuration needed
const summerTime = new kk_date('2024-08-23 10:00:00').tz('America/New_York'); // Automatically EDT
const winterTime = new kk_date('2024-12-23 10:00:00').tz('America/New_York'); // Automatically EST

console.log(summerTime.format('HH:mm')); // Summer time (EDT)
console.log(winterTime.format('HH:mm')); // Winter time (EST)

Memory-Efficient Operations

// Object pooling for high-frequency operations
const dates = [];
for (let i = 0; i < 10000; i++) {
    dates.push(new kk_date('2024-08-23 10:00:00'));
    // Memory usage remains constant due to object pooling
}

// Lazy loading - timezone data loaded only when needed
const date = new kk_date('2024-08-23 10:00:00');
// Timezone data not loaded until .tz() is called

Date Manipulation

const date = new kk_date('2024-08-23 10:30:00');

// Add/subtract time
date.add(2, 'hours');                   // Add 2 hours
date.add(-1, 'days');                   // Subtract 1 day
date.add(3, 'months');                  // Add 3 months

// Start/end of periods
date.startOf('months');                 // Start of month
date.endOf('weeks');                    // End of week

Comparison Operations

const date1 = new kk_date('2024-08-23');
const date2 = new kk_date('2024-08-25');

date1.isBefore(date2);                  // true
date1.isAfter(date2);                   // false
date1.isSame(date2);                    // false
// diff is measured as (other - this), so a later argument yields a positive result:
date1.diff(date2, 'days');              // 2
date2.diff(date1, 'days');              // -2

🔧 Configuration

// Global configuration
kk_date.setTimezone('UTC');
kk_date.config({ locale: 'en', weekStartDay: 1 }); // Monday

// Instance-specific configuration
const date = new kk_date('2024-08-23');
date.config({ 
    timezone: 'America/New_York',
    locale: 'tr',
    weekStartDay: 0
});

📱 React Native & Hermes Support

kk-date is compatible with React Native using the Hermes JavaScript engine.

Tested Environment:

Expo 54
React Native 0.81
Hermes engine enabled

What Works Out of the Box

All core features work without any additional configuration:

Date creation, formatting, and parsing
add, subtract, diff, startOf, endOf
isBefore, isAfter, isSame, isBetween
Timezone conversions (.tz())
fromNow, toNow relative time
Caching system

Hermes Intl Compatibility

Hermes has a known limitation with Intl.DateTimeFormat — the timeZoneName: 'longOffset' option either splits the GMT offset across multiple parts or is not supported at all. kk-date automatically detects and handles this with a built-in fallback:

// This works seamlessly on Hermes — no configuration needed
const date = new kk_date('2024-08-23 10:30:00');
const istanbul = date.tz('Europe/Istanbul');
console.log(istanbul.format('YYYY-MM-DD HH:mm')); // 2024-08-23 13:30

The fallback uses a date-comparison method to calculate timezone offsets when longOffset is unavailable, ensuring correct DST-aware results across all timezones.

Installation (React Native)

npm install kk-date

No polyfills or additional packages required.

// CommonJS (Metro bundler compatible)
const kk_date = require('kk-date');

const date = new kk_date('2024-08-23');
console.log(date.format('DD/MM/YYYY')); // 23/08/2024

🌍 Browser Support

Chrome 60+ (basic functionality)
Firefox 55+ (basic functionality)
Safari 12+ (basic functionality)
Edge 79+ (basic functionality)
Internet Explorer 11+ (with polyfills)

Advanced Features:

Locale Configuration: Chrome 74+, Firefox 75+, Safari 14.1+, Edge 79+
Relative Time Formatting: Chrome 71+, Firefox 65+, Safari 14.1+, Edge 79+ (with fallback)

Note: Basic date operations work in older browsers, but locale configuration requires newer Intl APIs.

📊 Performance Benchmarks

Note: All performance figures in this README come from our own benchmark suite on Node.js 26 and are reproduced by CI on every PR (the "Performance Benchmarks" job runs benchmark.js + benchmark2.js and uploads the results). They are not guarantees — results vary by workload, hardware, Node version, and caching. Reproduce locally with node benchmark.js / node benchmark2.js.

Real-World Sequential Operations (1000 days, 100 operations/day)

Our benchmark simulates real-world usage by processing 1000 sequential days with 100 operations per day. This reflects typical production scenarios where dates are processed in sequence rather than synthetic benchmarks.

Run the benchmark yourself:

node benchmark2.js

Representative run (Node.js 26) — reproduced by CI on every PR (see the "Performance Benchmarks" job artifacts). Numbers vary run-to-run. Totals are for 100,000 operations per scenario:

Operation	kk-date	Moment.js	Day.js	Luxon	vs Fastest Competitor
Date Creation & Formatting	190ms	1531ms	879ms	1190ms	~362% faster than Day.js
Time Operations	267ms	1759ms	712ms	3183ms	~166% faster than Day.js
Timezone Conversions	452ms	3509ms	23787ms	5036ms	~676% faster than Moment
Complex Operations	373ms	3404ms	1710ms	3718ms	~358% faster than Day.js

Overall Performance Summary

kk-date wins the overall sequential run and every individual scenario above.

Library	Total Time	Operations/sec	Performance
kk-date	1.28s	311,742 ops/sec	🏆 Winner
Moment.js	10.20s	39,206 ops/sec	~695% slower
Luxon	13.13s	30,471 ops/sec	~923% slower
Day.js	27.09s	14,767 ops/sec	~2011% slower

Memory & Bundle Size

Net heap delta after creating 100,000 date instances (from node benchmark.js). This metric is dominated by GC timing, so it is noisy and several libraries can show a negative net delta — it is not a unique kk-date property. Bundle sizes are the published package sizes.

Library	Heap Δ / 100k instances*	Bundle Size	DST Support
kk-date	~+15 MB	15 KB	Built-in
Moment.js	~-16 MB*	297 KB	Plugin required
Day.js	~-4 MB*	18.5 KB	Plugin required
Luxon	~+5 MB	71 KB	Built-in

_{* GC-timing artifact — varies run-to-run and can be negative for multiple libraries; reproduce with node benchmark.js.}

kk-date's real memory advantages come from object pooling, LRU cache eviction, and creating few intermediate objects — which keep long-running processes stable. The exact heap-delta number is not a guarantee.

// Measurement methodology:
const before = process.memoryUsage().heapUsed;
// Create 100,000 date instances...
const after = process.memoryUsage().heapUsed;
console.log((after - before) / 1024 / 1024, 'MB'); // GC-dependent; can be negative

Cache Performance Impact

Without Cache vs With Cache (representative run):

~32% faster repeated operations when cache is enabled
Average operation time: ~41ms → ~27ms with cache
Cache hit ratio: 100% for repeated operations

Memory overhead: minimal (caches are LRU-capped at 10,000 entries)

Why Enable Caching:

// Enable for high-performance scenarios
kk_date.caching({ status: true, defaultTtl: 3600 });

// Perfect for:
// ✅ Repeated timezone conversions (the biggest cache win)
// ✅ Frequently re-formatting the same inputs
// ✅ Large-scale data processing (handles 1M ops efficiently)
// ✅ Hot paths that re-convert/re-format the same instants

Key Performance Advantages

⚡ ~95% faster than the average of competing libraries (comprehensive benchmark)
🚀 up to ~98% faster in timezone operations (critical for global apps)
📊 Big-data ready - efficient for bulk/1M-operation workloads
💾 Stable memory - object pooling + LRU eviction; net heap delta is GC-dependent (often negative)
⚙️ ~32% boost with smart caching enabled
🌍 Over 50x faster (≈5200%) than Day.js in timezone conversions

✅ Production tested with 585 comprehensive tests

🤝 Contributing

We welcome contributions! Please see our Contributing Guide for details.

Running Tests

npm test                    # Run all tests
npm test -- --watch        # Run tests in watch mode
npm test -- --coverage     # Run tests with coverage

Running Benchmarks

node benchmark.js           # Run comprehensive benchmark suite
node benchmark2.js          # Run sequential 1000-day benchmark

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

Inspired by modern date libraries like Moment.js and Day.js
Built with performance and developer experience in mind
Comprehensive timezone support using IANA timezone database

📞 Support

🐛 Issues: GitHub Issues
📖 Documentation: Full Documentation
💬 Discussions: GitHub Discussions

⚠️ Disclaimer

This software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose, and noninfringement. Use of the kk-date package is at your own risk. The maintainers and contributors do not guarantee that the package will function without errors or produce accurate results in all scenarios. In no event shall the authors or contributors be held liable for any damages, losses, or issues arising from the use of this package.

🚀 What's Next?

We're constantly working to improve kk-date! Here are some exciting features we're planning:

🌐 Web Workers Support - Asynchronous date operations for better performance
📦 Tree Shaking - Bundle size optimization for production builds
🔌 Plugin System - Extensible architecture for custom functionality
🎯 Enhanced Caching - More intelligent cache strategies for specific use cases

✅ Template Compilation shipped: format() now compiles any token combination once and caches it — see the Formatting Guide.

💡 Pro Tips

Enable caching for applications with repeated timezone operations
Use instance configuration for date-specific settings
Monitor cache statistics in production for optimal performance
Test DST transitions thoroughly in your application
Consider memory usage for high-frequency operations

Made with ❤️ for the JavaScript community

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docs		docs
scripts		scripts
test		test
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
LICENSE		LICENSE
README.md		README.md
benchmark.js		benchmark.js
benchmark2.js		benchmark2.js
biome.json		biome.json
constants.js		constants.js
functions.js		functions.js
index.d.ts		index.d.ts
index.js		index.js
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kk-date - Advanced JavaScript Date Library

🌟 Why Choose kk-date?

Performance & Efficiency (measured on Node.js 26; reproduced by CI, results vary)

Reliability & Safety

Features & Compatibility

📦 Installation

🚨 Breaking Changes in v5.0.0

🚀 Quick Start

📚 Documentation

📖 Complete API Reference

🕐 Timezone Guide

📅 Formatting Guide

⚙️ Configuration Guide

⚡ Performance Guide

🔧 Advanced Usage

🧪 Testing Guide

🌍 Timezone Accuracy & Reliability

Why Timezone Accuracy Matters

kk-date vs Other Libraries

Real-World Example

Cross-Platform Consistency

Automatic DST Detection

Safety Comparison: kk-date vs Others

Why Other Libraries Fail

🎯 Performance & Reliability

🚀 Intelligent Caching System (~70% Performance Boost)

Zero-Config DST Handling

Memory-Efficient Operations

Date Manipulation

Comparison Operations

🔧 Configuration

📱 React Native & Hermes Support

What Works Out of the Box

Hermes Intl Compatibility

Installation (React Native)

🌍 Browser Support

📊 Performance Benchmarks

Real-World Sequential Operations (1000 days, 100 operations/day)

Overall Performance Summary

Memory & Bundle Size

Cache Performance Impact

Key Performance Advantages

🤝 Contributing

Running Tests

Running Benchmarks

📄 License

🙏 Acknowledgments

📞 Support

⚠️ Disclaimer

🚀 What's Next?

💡 Pro Tips

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