dayjs
2KB immutable date time library alternative to Moment.js with the same modern API
About
2KB immutable date time library alternative to Moment.js with the same modern API
Live mirror of the GitHub README. Updated whenever the repo's default branch changes.
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Fast 2kB alternative to Moment.js with the same modern API
Day.js is a minimalist JavaScript library that parses, validates, manipulates, and displays dates and times for modern browsers with a largely Moment.js-compatible API. If you use Moment.js, you already know how to use Day.js.
dayjs().startOf('month').add(1, 'day').set('year', 2018).format('YYYY-MM-DD HH:mm:ss');
- 🕒 Familiar Moment.js API & patterns
- 💪 Immutable
- 🔥 Chainable
- 🌐 I18n support
- 📦 2kb mini library
- 👫 All browsers supported
Getting Started
Documentation
You can find for more details, API, and other docs on day.js.org website.
Installation
npm install dayjs --save
API
It's easy to use Day.js APIs to parse, validate, manipulate, and display dates and times.
dayjs('2018-08-08') // parse
dayjs().format('{YYYY} MM-DDTHH:mm:ss SSS [Z] A') // display
dayjs().set('month', 3).month() // get & set
dayjs().add(1, 'year') // manipulate
dayjs().isBefore(dayjs()) // query
I18n
Day.js has great support for internationalization.
But none of them will be included in your build unless you use it.
import 'dayjs/locale/es' // load on demand
dayjs.locale('es') // use Spanish locale globally
dayjs('2018-05-05').locale('zh-cn').format() // use Chinese Simplified locale in a specific instance
Plugin
A plugin is an independent module that can be added to Day.js to extend functionality or add new features.
import advancedFormat from 'dayjs/plugin/advancedFormat' // load on demand
dayjs.extend(advancedFormat) // use plugin
dayjs().format('Q Do k kk X x') // more available formats
Sponsors
Support this project by becoming a sponsor. Your logo will show up here with a link to your website.
[Become a sponsor via Github] [Become a sponsor via OpenCollective]
Contributors
This project exists thanks to all the people who contribute.
Please give us a 💖 star 💖 to support us. Thank you.
And thank you to all our backers! 🙏
License
Day.js is licensed under a MIT License.
Quick facts
npm install dayjsHow Sourcemap Explorer detects dayjs
We catch dayjs from two complementary signals: bundled source paths and the embedded package.json. Modern bundlers (webpack, Vite, esbuild, Rollup, Turbopack) preserve the original node_modules/dayjs/ paths inside the JavaScript sourcemap's sources[] array — that's the canonical signal. When the matching package.json is also captured in sourcesContent[], we read the exact version field — patch number included. No regex guessing, no version inference.
- 1
Confirm the site exposes sourcemaps
In DevTools Network, check the response headers of any application script for `SourceMap` or `X-SourceMap`. Failing that, fetch the script's last 4 KB and look for a `//# sourceMappingURL=` comment.
- 2
Find the package in the bundle
Open DevTools → Network → reload. Click any application script and look at its sourcemap. Inside, search `sources[]` for entries matching `node_modules/dayjs/` — every match confirms the package is bundled. The matching `sourcesContent[i]` for `node_modules/dayjs/package.json` gives you the exact installed version.
- 3
Read the version directly from package.json
Run `jq -r '. as $m | $m.sources | to_entries[] | select(.value | endswith("node_modules/dayjs/package.json")) | $m.sourcesContent[.key] | fromjson | .version' bundle.js.map`. Sourcemap Explorer automates the same query in the popup.
Recent versions
FAQ
What is dayjs used for?
2KB immutable date time library alternative to Moment.js with the same modern API
How can I tell if a website is using dayjs?
Open the page in Chrome with the Sourcemap Explorer extension installed and read the Stack tab. We catch `dayjs` from two complementary signals: `node_modules/dayjs/` paths inside the JavaScript sourcemap, and the embedded `package.json` we read for exact-version detection. Without the extension you can do the same lookup manually in DevTools — the steps are listed in the "How Sourcemap Explorer detects" section above.
What is the latest version of dayjs?
1.11.20, as published on the npm registry. The "Recent versions" table on this page lists the most recent 8 releases with their release dates. Sourcemap Explorer reports the version actually bundled into a site, which can lag the latest release by months on real-world deployments.
Where can I read more?
Project homepage: https://day.js.org. Source code: https://github.com/iamkun/dayjs. Published on npm: https://www.npmjs.com/package/dayjs. Licensed as MIT.
Detected by Sourcemap Explorer
When a bundle ships sourcemaps, we read the embedded package.json for dayjs and report the precise version. Without sourcemaps, an import / require in the page's scripts is enough to flag it.