dayjs-clone

A tiny learning-project clone of Day.js: a chainable, mostly-immutable date library with a plugin system for extending core functionality.

Why this structure?

• src/core.ts — the MyDate class. Every manipulation method (add, subtract, startOf) returns a new instance instead of mutating this. This is the single biggest design decision in a date library — get it wrong and every consumer of your library will eventually get bitten by a shared-reference bug.
• src/plugin-system.ts — the extend() function. Plugins receive the MyDate class itself and patch its prototype. This keeps core.ts small while letting you ship optional features (relative time, timezones, custom parsing) as separate, tree-shakeable modules — exactly how Day.js keeps its core bundle at ~2KB.
• src/plugins/relativeTime.ts — an example plugin implementing .fromNow() (e.g. "3 hours ago"), showing the plugin pattern end to end, including how to use TypeScript's declare module to type-augment the core class from a plugin file.

Usage

import dayjsClone, { extend } from 'dayjs-clone';
import relativeTime from 'dayjs-clone/plugins/relativeTime';

const now = dayjsClone();
const nextWeek = now.add(7, 'day');
console.log(nextWeek.format('YYYY-MM-DD'));

extend(relativeTime);
console.log(now.subtract(2, 'hour').fromNow()); // "2 hours ago"

Scripts

| Command | What it does | |-----------------------|------------------------------------------------| | npm install | Install dependencies | | npm run test | Run the test suite once | | npm run test:watch | Run tests in watch mode | | npm run build | Bundle to dist/ (CJS + ESM + .d.ts) | | npm run typecheck | Type-check without emitting files | | npm run dev | Watch mode build |

Where to go next

1. Add more units to format() — day-of-week names (ddd), 12-hour clock (hh A), millisecond padding.
2. Add a diff() method — compute the difference between two dates in a given unit.
3. Add a locale plugin — swap month/weekday names based on a locale object, like Day.js's dayjs/locale/* files.
4. Add a UTC plugin — right now all getters use local time. A utc() plugin that swaps the internal getters is a good exercise in how much timezone handling complicates a "simple" date library.
5. Set up CI — GitHub Actions workflow running npm test and npm run typecheck on every push.
6. Publish to npm — once you're happy with the API, npm publish.