dayjs
v1.11.20 MIT2KB immutable date time library alternative to Moment.js with the same modern API
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About dayjs
Day.js is a lightweight, immutable JavaScript library designed for modern web development, offering a familiar API for date and time manipulation.
It aims to solve the complexity and large bundle size often associated with date libraries like Moment.js, providing a more performant and user-friendly alternative for developers who need robust date handling without significant overhead.
The library champions an immutable approach, ensuring that date objects are never modified in place, which prevents unexpected side effects in complex applications.
Day.js boasts a comprehensive API that mirrors Moment.js, including methods for parsing, validating, manipulating, and formatting dates, making the transition for existing Moment.js users seamless. Common operations like `dayjs().format('YYYY-MM-DD')` or `dayjs(date).add(1, 'day')` are straightforward.
With a minimal footprint of just 3.5 kB (gzipped), Day.js is ideal for performance-sensitive applications and front-end frameworks where bundle size is a critical concern. Its extensive plugin system allows for future expansion without bloating the core library.
While Day.js offers immense flexibility, developers should be aware that its core functionality is intentionally lean. Advanced features require importing specific plugins, which must be explicitly managed to maintain the small bundle size.
When to use
- When optimizing for front-end performance by minimizing JavaScript bundle size, given its 3.5 kB gzipped footprint.
- When migrating from Moment.js and requiring a familiar API for date parsing, manipulation, and formatting.
- When building applications that require immutable date objects to prevent side effects and ensure predictable state management.
- When needing to perform complex date calculations such as adding or subtracting time units with methods like `add()` and `subtract()`.
- When working within modern JavaScript environments that benefit from ES Modules and tree-shaking, as Day.js is designed for efficient code splitting.
- When extending date functionality with plugins for features like time zones or relative time, leveraging its modular architecture.
When NOT to use
- If your application exclusively requires basic date display without any manipulation, native JavaScript `Date` objects might suffice.
- If you require extensive, out-of-the-box internationalization without the need to explicitly import plugins for localization.
- When deep, complex temporal logic involving historical calendar systems or non-standard timekeeping is a primary requirement, consider alternatives with more specialized engines.
- If your project strictly prohibits any external dependencies, even lightweight ones, for date handling.
- When the exact historical accuracy of leap seconds and ultra-precise time synchronization is critical and not covered by available plugins.