Day.js vs flatpickr
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A small JavaScript library for working with dates and times, with an API similar to Moment.js.
Open source · MIT
A lightweight, dependency-free date and time picker for web pages.
The short answer
Choose Day.js if you need…
- JavaScript developers who used Moment.js and want a smaller library
- Front-end projects where bundle size matters
- Apps that need date formatting and simple date arithmetic
- Projects that need localized date output via locale files
Choose flatpickr if you need…
- Web developers who need a date or time input in a JavaScript app
- Teams that want to avoid adding large dependencies like jQuery or Bootstrap
- Projects that need date range selection
- Sites that must support many languages through its locale options
Side-by-side
| Day.js | flatpickr | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 48.7k | 16.5k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Install with a package manager | Install with a package manager |
| Main language | JavaScript | TypeScript |
| Last code update | 52 days ago | 2 years ago |
What each one is
Day.js
Day.js is a small JavaScript library (about 2kB, per the README) that parses, checks, changes, and formats dates and times. Its API is largely compatible with Moment.js, so people familiar with Moment.js can use it with little relearning. Its objects are immutable, so operations return new values instead of changing the original.
flatpickr
flatpickr is a JavaScript library that adds a date and time picker to a web page, so visitors can choose dates from a calendar popup instead of typing them. It is described as having no dependencies, so it does not require jQuery, Bootstrap, or moment.js. The README says it supports date and time input, range and multiple-date selection, and 51 locales.
Best for
Day.js
- JavaScript developers who used Moment.js and want a smaller library
- Front-end projects where bundle size matters
- Apps that need date formatting and simple date arithmetic
- Projects that need localized date output via locale files
flatpickr
- Web developers who need a date or time input in a JavaScript app
- Teams that want to avoid adding large dependencies like jQuery or Bootstrap
- Projects that need date range selection
- Sites that must support many languages through its locale options
Strengths
Day.js
- Small footprint (about 2kB according to the README)
- Familiar API for anyone who has used Moment.js
- Immutable and chainable, which makes code easier to reason about
flatpickr
- The README states it has no dependencies and a small footprint compared with other libraries
- Includes many built-in features such as ranges, multiple dates, week numbers, and 8 themes
- Documentation and demos are available at the project homepage
Not ideal for
Day.js
- Projects that need full timezone handling beyond what the README describes; the README does not detail timezone support, so check the docs first
- Non-JavaScript environments, since the library is written for JavaScript
- Users who need a graphical or no-code tool
flatpickr
- Projects that only need a plain browser date field, since native inputs need no library
- Teams needing a framework-specific component without a wrapper, since the README points to separate community wrappers for React, Vue, and others
- Older browsers outside the listed compatibility range, since the README lists IE9 and up as the baseline
Trade-offs
Day.js
- Some functionality is in optional plugins, which must be loaded separately
- Compatibility with Moment.js is described as largely, not complete, so some code may need changes
- Documentation and details live on the external site day.js.org rather than the README
flatpickr
- The README is truncated and gives limited detail on setup and API, so some specifics are unclear from this text alone
- Wrapper components for frameworks are maintained separately by other authors, so quality and update pace may vary
- Last push date is 2024-08-02, so recent maintenance activity should be checked before adopting it
Getting started
flatpickr
Clone the repository
git clone https://github.com/flatpickr/flatpickrFrequently asked questions
What is the difference between Day.js and flatpickr?
Day.js: A small JavaScript library for working with dates and times, with an API similar to Moment.js. flatpickr: A lightweight, dependency-free date and time picker for web pages. Day.js suits javascript developers who used moment.js and want a smaller library, while flatpickr suits web developers who need a date or time input in a javascript app.
Are Day.js and flatpickr free?
Day.js: Free and open source. flatpickr: Free and open source.
Is Day.js or flatpickr more popular?
Day.js has more GitHub stars (48.7k) than flatpickr (16.5k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to Day.js and flatpickr?
Other options people compare them with include Luxon, react-dates.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.