Day.js vs You Don't Need Moment.js
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 guide to replacing Moment.js with native JavaScript or lighter date libraries, plus an ESLint plugin.
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 You Don't Need Moment.js if you need…
- Developers maintaining a web app that loads Moment.js and wants a smaller bundle
- Teams planning a migration away from Moment.js who want a side-by-side reference
- Developers who only use a few simple Moment.js functions
- Projects that want to find Moment.js usages automatically via ESLint
Side-by-side
| Day.js | You Don't Need Moment.js | |
|---|---|---|
| Type | Library | Learning resource |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 48.7k | 13.3k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Install with a package manager | Install with a package manager |
| Main language | JavaScript | JavaScript |
| Last code update | 52 days ago | 10 months 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.
You Don't Need Moment.js
This is a reference guide, not a runnable program. It lists common date and time tasks (parsing, formatting, adding and subtracting, comparing) and shows how to do each one without Moment.js, using native JavaScript or smaller libraries such as date-fns and dayjs. It also includes a comparison table and an ESLint plugin that flags places in your code where Moment.js may not be needed.
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
You Don't Need Moment.js
- Developers maintaining a web app that loads Moment.js and wants a smaller bundle
- Teams planning a migration away from Moment.js who want a side-by-side reference
- Developers who only use a few simple Moment.js functions
- Projects that want to find Moment.js usages automatically via ESLint
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
You Don't Need Moment.js
- Clear, organized list of common date tasks with alternatives for each
- Includes a feature parity table against native JavaScript and Temporal
- Provides an ESLint plugin to help find code that could drop Moment.js
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
You Don't Need Moment.js
- Projects that rely heavily on Moment.js timezone features, since the README says Moment.js timezone support is good via moment-timezone and suggests this guide is for apps not using timezones
- Developers looking for a single drop-in library, since the guide covers several alternatives rather than recommending one
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
You Don't Need Moment.js
- The README is truncated in this data, so not every function's details could be verified here
- The comparison table's size and star figures are badge links that may change over time
Getting started
You Don't Need Moment.js
Install the ESLint plugin as a dev dependency
npm install --save-dev eslint-plugin-you-dont-need-momentjsFrequently asked questions
What is the difference between Day.js and You Don't Need Moment.js?
Day.js: A small JavaScript library for working with dates and times, with an API similar to Moment.js. You Don't Need Moment.js: A guide to replacing Moment.js with native JavaScript or lighter date libraries, plus an ESLint plugin. Day.js suits javascript developers who used moment.js and want a smaller library, while You Don't Need Moment.js suits developers maintaining a web app that loads moment.js and wants a smaller bundle.
Are Day.js and You Don't Need Moment.js free?
Day.js: Free and open source. You Don't Need Moment.js: Free and open source.
Is Day.js or You Don't Need Moment.js more popular?
Day.js has more GitHub stars (48.7k) than You Don't Need Moment.js (13.3k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to Day.js and You Don't Need Moment.js?
Other options people compare them with include Luxon, flatpickr.
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.