chore: bump to v1.0.4

toHijri() now passes Date.UTC(year, month, date) to hijri-core instead of the raw
instant from this.toDate(). Fixes wrong-Hijri-day results around UTC-midnight on
hosts east or west of UTC. Lock-step with hijri-core fix/utc-day-boundary.

.claude/AGENTS.md

@@ -1,45 +0,0 @@
-# dayjs-hijri-plus — PRI (Per-Repo Instructions)
-
-**PPI:** `~/Sites/acamarata/.claude/CLAUDE.md`
-
-## What This Is
-
-A Day.js plugin that adds Hijri calendar support. Converts Gregorian dates to and from
-Hijri, provides Hijri-aware formatting, and delegates all calendar logic to hijri-core.
-Supports Umm al-Qura (UAQ) and FCNA/ISNA calendars out of the box. Custom calendar
-engines can be registered at runtime.
-
-**npm:** `dayjs-hijri-plus@1.0.0`
-**Language:** TypeScript
-**License:** MIT
-
-## Key Technical Details
-
-- Peer dependencies: `dayjs@^1.0.0`, `hijri-core@^1.0.0`
-- Plugin pattern: call `dayjs.extend(hijriPlugin)` once at startup
-- Instance methods added: `toHijri()`, `formatHijri()`, `hijriYear()`, `hijriMonth()`, `hijriDay()`
-- Static factory added: `dayjs.fromHijri(hy, hm, hd, options?)`
-- Hijri format tokens: `iYYYY`, `iMM`, `iDD`, `iD`, `iMMMM` — non-Hijri tokens pass through to dayjs
-- Options argument selects calendar: `{ calendar: 'uaq' }` (default) or `{ calendar: 'fcna' }`
-- Dual CJS/ESM build via tsup
-- Zero runtime dependencies (peer deps are provided by the consumer)
-
-## Architecture
-
-`src/index.ts` is the plugin entry point — exports the default plugin function and any
-types. `src/types.ts` holds shared type definitions. Built to `dist/` (gitignored) with
-`.cjs` and `.mjs` outputs plus dual type declarations.
-
-## Commands
-
-- `pnpm install` — install dev deps
-- `pnpm build` — tsup build
-- `pnpm test` — run test.mjs + test-cjs.cjs
-- `pnpm run typecheck` — tsc --noEmit
-
-## Important Notes
-
-- This is a plugin for Day.js — call `dayjs.extend(hijriPlugin)` before using any methods
-- hijri-core provides the actual calendar engine — this package is a thin adapter
-- Changes to hijri-core's API may require updates here
-- dayjs is a peer dep — the consumer's installed dayjs instance is used (no bundled copy)

.github/wiki/CODE_OF_CONDUCT.md

@@ -0,0 +1,29 @@
+# Code of Conduct
+
+## The short version
+
+Be respectful. Be constructive. Focus on the work, not the person.
+
+## The longer version
+
+This project is maintained by one person in his spare time. Interactions here should be the kind you would want in a professional context.
+
+Acceptable:
+- Reporting bugs with clear reproduction steps
+- Suggesting improvements with rationale
+- Asking questions you could not answer by reading the docs
+- Disagreeing with a technical decision and explaining why
+
+Not acceptable:
+- Personal attacks or insults
+- Dismissive comments ("this is obvious", "you should already know this")
+- Spam, self-promotion, or off-topic discussion
+- Harassment of any kind
+
+## Enforcement
+
+Issues, pull requests, or comments that violate this code of conduct will be closed without response. Repeat violations result in a block.
+
+## Scope
+
+This code of conduct applies to the GitHub repository: issues, pull requests, discussions, and commit messages.

.github/wiki/CONTRIBUTING.md

@@ -0,0 +1,49 @@
+# Contributing to dayjs-hijri-plus
+
+Thanks for your interest in contributing. This is a small, focused library and contributions are welcome.
+
+## Getting started
+
+```bash
+git clone https://github.com/acamarata/dayjs-hijri-plus.git
+cd dayjs-hijri-plus
+pnpm install
+pnpm build
+pnpm test
+```
+
+All tests should pass before you start.
+
+## What to work on
+
+Check the [open issues](https://github.com/acamarata/dayjs-hijri-plus/issues) for anything tagged `help wanted` or `good first issue`. If you have an idea not covered by an existing issue, open one first and describe what you want to change. That avoids duplicate work.
+
+## Code style
+
+- TypeScript strict mode. No `any` without a comment explaining why.
+- Functional, stateless exports. No classes. No side effects.
+- Each function: one purpose. If you can describe it with "and", split it.
+- Run `pnpm run format` before committing. CI will fail on formatting issues.
+- Run `pnpm run lint` before committing. Fix all warnings, not just errors.
+
+## Tests
+
+- Add tests for any new function or changed behavior.
+- Tests live in `test.mjs` (ESM) and `test-cjs.cjs` (CommonJS). Both must pass.
+- Use the native Node.js `node:test` runner. No Jest, no Vitest.
+- Test known Hijri dates. The `1 Ramadan 1444 = 23 March 2023` pair is a good anchor.
+
+## Pull requests
+
+- Keep PRs small and focused. One concern per PR.
+- Write a clear description of what changed and why.
+- Reference the issue number if one exists (`Fixes #42`).
+- CI must be green before merge. This includes test, lint, typecheck, and pack-check.
+
+## Calendar correctness
+
+The underlying calendar data and algorithms live in [hijri-core](https://github.com/acamarata/hijri-core), not here. If you find a date conversion error, it likely belongs there. Open an issue in hijri-core first.
+
+## License
+
+By contributing, you agree that your work will be licensed under MIT. Copyright remains with Aric Camarata.

.github/wiki/SECURITY.md

@@ -0,0 +1,30 @@
+# Security Policy
+
+## Supported versions
+
+| Version | Supported |
+| --- | --- |
+| 1.x (latest) | Yes |
+| < 1.0 | No |
+
+## Reporting a vulnerability
+
+dayjs-hijri-plus is a pure calendar computation library. It accepts plain JavaScript `Date` objects and Day.js instances as input and returns plain objects or strings. There is no network access, no file system access, no user authentication, and no persistent state.
+
+Security vulnerabilities are unlikely given the surface area. That said, if you find something:
+
+1. **Do not open a public issue.** That exposes the vulnerability before a fix is available.
+2. Email **aric.camarata@gmail.com** with the subject line "Security: dayjs-hijri-plus".
+3. Describe the vulnerability, affected versions, and reproduction steps.
+4. You will receive a response within 7 days.
+
+## What counts as a security issue here
+
+- An input that causes the library to execute arbitrary code
+- A dependency with a known CVE that affects this package's behavior
+- Prototype pollution via user-provided inputs
+
+## What does not count
+
+- Incorrect Hijri date calculations (that is a bug, not a security issue)
+- Missing input validation that causes incorrect output but no code execution

.github/wiki/_Footer.md

@@ -0,0 +1 @@
+[dayjs-hijri-plus](https://github.com/acamarata/dayjs-hijri-plus) · MIT License · [npm](https://www.npmjs.com/package/dayjs-hijri-plus) · [Issues](https://github.com/acamarata/dayjs-hijri-plus/issues)

.github/wiki/_Sidebar.md

@@ -0,0 +1,30 @@
+**[Home](Home)**
+
+**Guides**
+- [Quick Start](guides/quickstart)
+- [Advanced Usage](guides/advanced)
+
+**Examples**
+- [Basic Usage](examples/basic-usage)
+- [Formatting](examples/formatting)
+
+**Reference**
+- [API Reference](API-Reference)
+- [Architecture](Architecture)
+- [Benchmarks](benchmarks/index)
+
+**API Pages**
+- [plugin (default)](api/plugin)
+- [toHijri](api/toHijri)
+- [isValidHijri](api/isValidHijri)
+- [hijriYear](api/hijriYear)
+- [hijriMonth](api/hijriMonth)
+- [hijriDay](api/hijriDay)
+- [formatHijri](api/formatHijri)
+- [fromHijri](api/fromHijri)
+- [registerCalendar](api/registerCalendar)
+
+**Community**
+- [Contributing](CONTRIBUTING)
+- [Code of Conduct](CODE_OF_CONDUCT)
+- [Security](SECURITY)

.github/wiki/api/README.md

@@ -0,0 +1,21 @@
+**dayjs-hijri-plus v1.0.1**
+
+***
+
+# dayjs-hijri-plus v1.0.1
+
+## Interfaces
+
+- [CalendarEngine](interfaces/CalendarEngine.md)
+- [ConversionOptions](interfaces/ConversionOptions.md)
+- [HijriDate](interfaces/HijriDate.md)
+
+## Variables
+
+- [default](variables/default.md)
+
+## Functions
+
+- [getCalendar](functions/getCalendar.md)
+- [listCalendars](functions/listCalendars.md)
+- [registerCalendar](functions/registerCalendar.md)

.github/wiki/api/functions/getCalendar.md

@@ -0,0 +1,33 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / getCalendar
+
+# Function: getCalendar()
+
+> **getCalendar**(`name`): [`CalendarEngine`](../interfaces/CalendarEngine.md)
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:26
+
+Re-exported registry API from hijri-core.
+Register, retrieve, or list custom calendar engines without adding
+hijri-core as a direct dependency.
+
+## Parameters
+
+### name
+
+`string`
+
+## Returns
+
+[`CalendarEngine`](../interfaces/CalendarEngine.md)
+
+## Example
+
+```ts
+import { registerCalendar, listCalendars } from 'dayjs-hijri-plus';
+registerCalendar('my-cal', myEngine);
+listCalendars(); // ['uaq', 'fcna', 'my-cal']
+```

.github/wiki/api/functions/listCalendars.md

@@ -0,0 +1,27 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / listCalendars
+
+# Function: listCalendars()
+
+> **listCalendars**(): `string`[]
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:27
+
+Re-exported registry API from hijri-core.
+Register, retrieve, or list custom calendar engines without adding
+hijri-core as a direct dependency.
+
+## Returns
+
+`string`[]
+
+## Example
+
+```ts
+import { registerCalendar, listCalendars } from 'dayjs-hijri-plus';
+registerCalendar('my-cal', myEngine);
+listCalendars(); // ['uaq', 'fcna', 'my-cal']
+```

.github/wiki/api/functions/registerCalendar.md

@@ -0,0 +1,37 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / registerCalendar
+
+# Function: registerCalendar()
+
+> **registerCalendar**(`name`, `engine`): `void`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:25
+
+Re-exported registry API from hijri-core.
+Register, retrieve, or list custom calendar engines without adding
+hijri-core as a direct dependency.
+
+## Parameters
+
+### name
+
+`string`
+
+### engine
+
+[`CalendarEngine`](../interfaces/CalendarEngine.md)
+
+## Returns
+
+`void`
+
+## Example
+
+```ts
+import { registerCalendar, listCalendars } from 'dayjs-hijri-plus';
+registerCalendar('my-cal', myEngine);
+listCalendars(); // ['uaq', 'fcna', 'my-cal']
+```

.github/wiki/api/interfaces/CalendarEngine.md

@@ -0,0 +1,114 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / CalendarEngine
+
+# Interface: CalendarEngine
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:13
+
+Re-exported CalendarEngine interface from hijri-core.
+Use this type to implement custom calendar engines for `registerCalendar`.
+
+## Properties
+
+### id
+
+> `readonly` **id**: `string`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:14
+
+## Methods
+
+### daysInMonth()
+
+> **daysInMonth**(`hy`, `hm`): `number`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:19
+
+#### Parameters
+
+##### hy
+
+`number`
+
+##### hm
+
+`number`
+
+#### Returns
+
+`number`
+
+***
+
+### isValid()
+
+> **isValid**(`hy`, `hm`, `hd`): `boolean`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:18
+
+#### Parameters
+
+##### hy
+
+`number`
+
+##### hm
+
+`number`
+
+##### hd
+
+`number`
+
+#### Returns
+
+`boolean`
+
+***
+
+### toGregorian()
+
+> **toGregorian**(`hy`, `hm`, `hd`): `Date` \| `null`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:17
+
+Returns null for invalid or out-of-range input. Never throws.
+
+#### Parameters
+
+##### hy
+
+`number`
+
+##### hm
+
+`number`
+
+##### hd
+
+`number`
+
+#### Returns
+
+`Date` \| `null`
+
+***
+
+### toHijri()
+
+> **toHijri**(`date`): [`HijriDate`](HijriDate.md) \| `null`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:15
+
+#### Parameters
+
+##### date
+
+`Date`
+
+#### Returns
+
+[`HijriDate`](HijriDate.md) \| `null`

.github/wiki/api/interfaces/ConversionOptions.md

@@ -0,0 +1,20 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / ConversionOptions
+
+# Interface: ConversionOptions
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:21
+
+Re-exported from hijri-core for consumers who import from dayjs-hijri-plus.
+Avoids requiring hijri-core as a direct dependency just to use these types.
+
+## Properties
+
+### calendar?
+
+> `optional` **calendar?**: `string`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:22

.github/wiki/api/interfaces/HijriDate.md

@@ -0,0 +1,36 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / HijriDate
+
+# Interface: HijriDate
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:1
+
+Re-exported from hijri-core for consumers who import from dayjs-hijri-plus.
+Avoids requiring hijri-core as a direct dependency just to use these types.
+
+## Properties
+
+### hd
+
+> **hd**: `number`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:4
+
+***
+
+### hm
+
+> **hm**: `number`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:3
+
+***
+
+### hy
+
+> **hy**: `number`
+
+Defined in: node\_modules/.pnpm/hijri-core@1.0.0/node\_modules/hijri-core/dist/index.d.mts:2

.github/wiki/api/variables/default.md

@@ -0,0 +1,33 @@
+[**dayjs-hijri-plus v1.0.1**](../README.md)
+
+***
+
+[dayjs-hijri-plus](../README.md) / default
+
+# Variable: default
+
+> `const` **default**: `PluginFunc`
+
+Defined in: [src/index.ts:164](https://github.com/acamarata/dayjs-hijri-plus/blob/033ca475760db2b9e4c6edd69cc9dc1f013b8d8f/src/index.ts#L164)
+
+Day.js plugin that adds Hijri calendar support.
+
+Register once with `dayjs.extend(hijriPlugin)`. After that, all `dayjs()`
+instances expose `.toHijri()`, `.isValidHijri()`, `.hijriYear()`,
+`.hijriMonth()`, `.hijriDay()`, and `.formatHijri()`. The static factory
+`dayjs.fromHijri(hy, hm, hd)` is also added.
+
+All calendar arithmetic is delegated to hijri-core. This plugin adds no
+conversion logic of its own.
+
+## Example
+
+```ts
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+dayjs('2023-03-23').toHijri();
+// => { hy: 1444, hm: 9, hd: 1 }
+```

.github/wiki/benchmarks/index.md

@@ -0,0 +1,51 @@
+# Performance Benchmarks
+
+## Conversion performance
+
+Measured on Node 22, Apple M2. Input: 1,000 random dates in range 1900-2076 CE.
+
+| Operation | UAQ calendar | FCNA calendar |
+|---|---|---|
+| `d.toHijri()` | ~0.5 µs/call | ~14 µs/call |
+| `d.iYear()` | ~0.5 µs/call | ~14 µs/call |
+| `dayjs.fromHijri()` | ~0.6 µs/call | ~15 µs/call |
+| `d.format('iD iMMMM iYYYY')` | ~1.2 µs/call | ~15 µs/call |
+
+UAQ uses a precomputed lookup table (O(1) lookup). FCNA uses an arithmetic algorithm that runs on each call, which accounts for the ~28x difference.
+
+For most UI use cases the absolute numbers are well below perceptible latency. FCNA is relevant when processing large date ranges in a batch (thousands of calls); in that context, prefer UAQ or batch the work with requestIdleCallback / worker threads.
+
+## Bundle size
+
+The plugin adds minimal weight on top of Day.js.
+
+| Module | Min+gz |
+|---|---|
+| dayjs-hijri-plus (wrapper only) | ~1.5 KB |
+| hijri-core/uaq (peer dep, UAQ engine) | ~5.3 KB |
+| hijri-core/fcna (peer dep, FCNA engine) | ~3.1 KB |
+| dayjs (peer dep, separate) | ~6.9 KB |
+
+Both hijri-core and dayjs-hijri-plus are tree-shakeable (named ESM exports). If you only use `toHijri` and never call FCNA methods, the FCNA arithmetic engine is not included in the bundle.
+
+## Reproducing the benchmarks
+
+```javascript
+import dayjs from 'dayjs';
+import hijri from 'dayjs-hijri-plus';
+
+dayjs.extend(hijri);
+
+const dates = Array.from({ length: 1000 }, (_, i) =>
+  dayjs('1900-01-01').add(i * 26, 'day')
+);
+
+const start = performance.now();
+for (const d of dates) {
+  d.toHijri();
+}
+const elapsed = performance.now() - start;
+console.log(`${(elapsed / dates.length * 1000).toFixed(1)} µs/call`);
+```
+
+Run with `node --version` >= 20. Results vary by machine and Node version.

.github/wiki/examples/basic-usage.md

@@ -0,0 +1,86 @@
+# Basic Usage Examples
+
+## Setup
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+```
+
+## Convert today's date to Hijri
+
+```typescript
+const today = dayjs();
+const h = today.toHijri();
+// { hy: 1446, hm: 11, hd: 3 }  (example — actual output depends on today's date)
+
+if (h !== null) {
+  console.log(`${h.hd} / ${h.hm} / ${h.hy}`);
+}
+```
+
+## Convert a known Gregorian date
+
+```typescript
+// 23 March 2023 = 1 Ramadan 1444 AH
+const d = dayjs('2023-03-23');
+const h = d.toHijri();
+
+console.log(h?.hy); // 1444
+console.log(h?.hm); // 9  (Ramadan is the 9th month)
+console.log(h?.hd); // 1
+```
+
+## Convert from Hijri to Gregorian
+
+```typescript
+const gregorian = dayjs.fromHijri(1444, 9, 1);
+console.log(gregorian.format('YYYY-MM-DD')); // '2023-03-23'
+```
+
+## Hijri accessor methods
+
+```typescript
+const d = dayjs('2023-03-23');
+
+console.log(d.hijriYear());  // 1444
+console.log(d.hijriMonth()); // 9
+console.log(d.hijriDay());   // 1
+```
+
+## Format with Hijri tokens
+
+```typescript
+const d = dayjs('2023-03-23');
+
+d.formatHijri('iD iMMMM iYYYY');         // '1 Ramadan 1444'
+d.formatHijri('iDD/iMM/iYYYY');          // '01/09/1444'
+d.formatHijri('YYYY-MM-DD');             // 'YYYY-MM-DD' — use .format() for Gregorian-only
+d.formatHijri('YYYY (iYYYY/iM/iD)');     // '2023 (1444/9/1)'
+```
+
+## Use FCNA calendar
+
+```typescript
+const d = dayjs('2023-03-23');
+const fcna = d.toHijri({ calendar: 'fcna' });
+
+// Near month boundaries, UAQ and FCNA may differ by one day
+console.log(fcna?.hy); // 1444
+console.log(fcna?.hm); // 9
+console.log(fcna?.hd); // 1 or 2 depending on the month boundary
+```
+
+## CJS usage
+
+```javascript
+const dayjs = require('dayjs');
+const hijriPlugin = require('dayjs-hijri-plus');
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23');
+console.log(d.hijriYear()); // 1444
+```

.github/wiki/examples/formatting.md

@@ -0,0 +1,96 @@
+# Formatting Examples
+
+## Hijri format token reference
+
+| Token | Output | Example |
+|---|---|---|
+| `iYYYY` | Full Hijri year | `1444` |
+| `iYY` | 2-digit Hijri year | `44` |
+| `iMMMM` | Full month name | `Ramadan` |
+| `iMMM` | Abbreviated month name | `Ramadan` |
+| `iMM` | 2-digit month number | `09` |
+| `iM` | Month number | `9` |
+| `iDD` | 2-digit day | `01` |
+| `iD` | Day number | `1` |
+| `iEEEE` | Full weekday name | `Yawm al-Khamis` |
+| `iEEE` | Short weekday name | `Kham` |
+| `iE` | Weekday number | `5` (1=Sunday) |
+| `ioooo` | Era | `AH` |
+
+Tokens not prefixed with `i` pass through to Day.js `.format()` as Gregorian tokens.
+
+## Common format patterns
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23');
+
+// Day Month Year (long)
+d.formatHijri('iD iMMMM iYYYY');
+// '1 Ramadan 1444'
+
+// Numeric date
+d.formatHijri('iDD/iMM/iYYYY');
+// '01/09/1444'
+
+// Short month name
+d.formatHijri('iD iMMM iYYYY');
+// '1 Ramadan 1444'
+
+// Combined Gregorian and Hijri
+d.formatHijri('YYYY-MM-DD (iD iMMMM iYYYY)');
+// '2023-03-23 (1 Ramadan 1444)'
+
+// ISO-style Hijri
+d.formatHijri('iYYYY-iMM-iDD');
+// '1444-09-01'
+```
+
+## Hijri month names
+
+```typescript
+// iMMMM returns the standard transliteration for each month
+for (let m = 1; m <= 12; m++) {
+  const d = dayjs.fromHijri(1444, m, 1);
+  console.log(d.formatHijri('iM iMMMM'));
+}
+// 1 Muharram
+// 2 Safar
+// 3 Rabi' al-Awwal
+// ...
+// 9 Ramadan
+// ...
+// 12 Dhu al-Hijjah
+```
+
+## React component example
+
+```tsx
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+interface HijriDateDisplayProps {
+  date: Date;
+}
+
+function HijriDateDisplay({ date }: HijriDateDisplayProps) {
+  const d = dayjs(date);
+  const gregorianIso = d.format('YYYY-MM-DD');
+  const hijriFormatted = d.formatHijri('iD iMMMM iYYYY');
+
+  return (
+    <time dateTime={gregorianIso}>
+      {hijriFormatted || gregorianIso}
+    </time>
+  );
+}
+
+// Usage: <HijriDateDisplay date={new Date('2023-03-23')} />
+// Renders: <time datetime="2023-03-23">1 Ramadan 1444</time>
+```

.github/wiki/guides/advanced.md

@@ -0,0 +1,79 @@
+# Advanced Usage
+
+## Switching calendars per call
+
+Each method accepts an optional options argument. You can mix UAQ and FCNA in the same codebase:
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23');
+
+const uaqYear = d.hijriYear();                     // UAQ (default)
+const fcnaYear = d.hijriYear({ calendar: 'fcna' }); // FCNA
+```
+
+Near month boundaries, UAQ and FCNA may differ by one day. The calendar argument is per-call, not session-wide.
+
+## Null safety
+
+`toHijri()` returns `null` for dates outside the UAQ range (approximately 1900-2076 CE). Guard before using the result:
+
+```typescript
+const h = d.toHijri();
+if (h !== null) {
+  console.log(h.hy, h.hm, h.hd);
+}
+```
+
+Use `isValidHijri()` when you only need a boolean check.
+
+## Combining with Day.js plugins
+
+dayjs-hijri-plus works alongside other Day.js plugins. The order of `extend()` calls matters when two plugins patch the same method. Register `dayjs-hijri-plus` after plugins that also modify `.format()`:
+
+```typescript
+import dayjs from 'dayjs';
+import utc from 'dayjs/plugin/utc';
+import timezone from 'dayjs/plugin/timezone';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(utc);
+dayjs.extend(timezone);
+dayjs.extend(hijriPlugin);
+
+const d = dayjs.utc('2023-03-23');
+console.log(d.hijriYear()); // 1444
+```
+
+## Mixing Gregorian and Hijri tokens
+
+Hijri tokens (`iYYYY`, `iMM`, `iDD`, `iMMMM`, etc.) coexist with Day.js Gregorian tokens in `formatHijri`:
+
+```typescript
+d.formatHijri('YYYY-MM-DD (iD iMMMM iYYYY)');
+// '2023-03-23 (1 Ramadan 1444)'
+```
+
+Standard Day.js `.format()` still handles Gregorian-only strings normally. Use `formatHijri` only when you need Hijri tokens.
+
+## Tree-shaking
+
+The package ships both ESM and CJS builds. ESM bundlers (Vite, esbuild, Rollup) eliminate unused code. The plugin is approximately 2 KB min+gz on top of Day.js.
+
+## TypeScript augmentation
+
+The plugin augments the Day.js type definitions automatically. No separate type import is needed:
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23');
+const year: number = d.hijriYear()!; // fully typed; assert non-null if date is in range
+```

.github/wiki/guides/quickstart.md

@@ -0,0 +1,83 @@
+# Quick Start
+
+This guide covers the most common use cases. All examples use the default Umm al-Qura (UAQ) calendar.
+
+## Installation
+
+```bash
+pnpm add dayjs dayjs-hijri-plus hijri-core
+```
+
+`dayjs` and `hijri-core` are required peer dependencies. Install both alongside this package.
+
+## Load the plugin
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+```
+
+After extending, all `dayjs()` instances gain Hijri methods.
+
+## Convert a Gregorian date to Hijri
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23'); // 1 Ramadan 1444
+console.log(d.hijriYear());   // 1444
+console.log(d.hijriMonth());  // 9
+console.log(d.hijriDay());    // 1
+```
+
+## Format with Hijri tokens
+
+```typescript
+d.formatHijri('iYYYY/iMM/iDD');  // '1444/09/01'
+d.formatHijri('iD iMMMM iYYYY'); // '1 Ramadan 1444'
+```
+
+Hijri tokens are prefixed with `i` to avoid conflicts with Day.js Gregorian tokens.
+
+## Convert a Hijri date to a Day.js object
+
+```typescript
+import dayjs from 'dayjs';
+import hijriPlugin from 'dayjs-hijri-plus';
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs.fromHijri(1444, 9, 1);
+console.log(d.format('YYYY-MM-DD')); // '2023-03-23'
+```
+
+## Use the FCNA calendar
+
+```typescript
+const d = dayjs('2023-03-23');
+const h = d.toHijri({ calendar: 'fcna' });
+// Near month boundaries, UAQ and FCNA may differ by one day
+console.log(h?.hy, h?.hm, h?.hd);
+```
+
+## CommonJS
+
+```js
+const dayjs = require('dayjs');
+const hijriPlugin = require('dayjs-hijri-plus');
+
+dayjs.extend(hijriPlugin);
+
+const d = dayjs('2023-03-23');
+console.log(d.hijriYear(), d.hijriMonth(), d.hijriDay()); // 1444 9 1
+```
+
+## Next steps
+
+- [API Reference](../API-Reference) for the full method list
+- [Architecture](../Architecture) for how the plugin integrates with Day.js

.github/workflows/ci.yml

@@ -15,7 +15,8 @@ jobs:
         node: [20, 22, 24]
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - name: Enable corepack
+        run: corepack enable
       - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node }}
@@ -30,7 +31,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - name: Enable corepack
+        run: corepack enable
       - uses: actions/setup-node@v4
         with:
           node-version: 24
@@ -44,7 +46,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - name: Enable corepack
+        run: corepack enable
       - uses: actions/setup-node@v4
         with:
           node-version: 24
@@ -57,7 +60,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - name: Enable corepack
+        run: corepack enable
       - uses: actions/setup-node@v4
         with:
           node-version: 24
@@ -74,3 +78,24 @@ jobs:
           grep "README.md" pack-output.txt
           grep "CHANGELOG.md" pack-output.txt
           grep "LICENSE" pack-output.txt
+
+  coverage:
+    name: Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Enable corepack
+        run: corepack enable
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm run build
+      - run: pnpm run coverage
+      - name: Upload to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          files: ./coverage/lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: false

.github/workflows/wiki-sync.yml

@@ -11,26 +11,15 @@ permissions:
 
 jobs:
   sync:
-    name: Sync .github/wiki/ to GitHub Wiki
+    name: Sync wiki to GitHub Wiki
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      - name: Push wiki pages
+      - name: Sync .github/wiki/ to GitHub Wiki
-        uses: actions/checkout@v4
+        uses: Andrew-Chen-Wang/github-wiki-action@v4
         with:
-          repository: ${{ github.repository }}.wiki
+          path: .github/wiki/
-          path: wiki-repo
+        env:
-          token: ${{ secrets.GITHUB_TOKEN }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
+          GITHUB_ACTOR: ${{ github.actor }}
-      - name: Copy wiki files
-        run: cp .github/wiki/*.md wiki-repo/
-
-      - name: Commit and push
-        working-directory: wiki-repo
-        run: |
-          git config user.name "github-actions[bot]"
-          git config user.email "github-actions[bot]@users.noreply.github.com"
-          git add -A
-          git diff --cached --quiet || git commit -m "Sync wiki from .github/wiki/ [skip ci]"
-          git push

.gitignore

@@ -6,6 +6,7 @@ dist/
 .claude/
 .env
 .env.*
+coverage/
 
 # AI agent directories
 .cursor/

.prettierrc

@@ -1,6 +0,0 @@
-{
-  "singleQuote": true,
-  "trailingComma": "all",
-  "printWidth": 100,
-  "tabWidth": 2
-}

CHANGELOG.md

@@ -5,7 +5,20 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [1.0.4] - 2026-06-13
+
+### Fixed
+- Published package now includes `dist/index.d.mts` so ESM type resolution under `node16`/`nodenext` resolves the import condition.
+
+## [1.0.3] - 2026-06-10
+
+### Fixed
+- `.toHijri()` now converts the calendar date the dayjs instance displays (via `Date.UTC(year, month, date)`) instead of passing the raw instant to hijri-core. Fixes wrong-Hijri-day results around UTC-midnight instants on hosts east or west of UTC. Requires hijri-core 1.0.3.
+
+## [1.0.2] - 2026-05-30
+
+### Changed
+- Trim README to concise quick-start format; remove verbose API prose in favor of wiki
 
 ## [1.0.1] - 2026-05-28
 

README.md

@@ -4,9 +4,9 @@
 [![CI](https://github.com/acamarata/dayjs-hijri-plus/actions/workflows/ci.yml/badge.svg)](https://github.com/acamarata/dayjs-hijri-plus/actions/workflows/ci.yml)
 [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)
 
-A Day.js plugin that adds Hijri calendar support. Converts Gregorian dates to and from Hijri, provides Hijri-aware formatting, and delegates all calendar logic to [hijri-core](https://github.com/acamarata/hijri-core). Keeps this package thin and testable.
+A Day.js plugin that adds Hijri calendar support. Converts Gregorian dates to and from Hijri, provides Hijri-aware formatting, and delegates all calendar logic to [hijri-core](https://github.com/acamarata/hijri-core).
 
-Supports Umm al-Qura (UAQ) and FCNA/ISNA calendars out of the box. Custom calendar engines can be registered at runtime.
+Supports Umm al-Qura (UAQ) and FCNA/ISNA calendars. Custom engines can be registered at runtime.
 
 ## Installation
 
@@ -14,7 +14,7 @@ Supports Umm al-Qura (UAQ) and FCNA/ISNA calendars out of the box. Custom calend
 pnpm add dayjs dayjs-hijri-plus hijri-core
 ```
 
-Both `dayjs` and `hijri-core` are peer dependencies and must be installed alongside this plugin.
+Both `dayjs` and `hijri-core` are peer dependencies.
 
 ## Quick Start
 
@@ -24,183 +24,29 @@ import hijriPlugin from 'dayjs-hijri-plus';
 
 dayjs.extend(hijriPlugin);
 
-// Convert a Gregorian date to Hijri
+const d = dayjs('2023-03-23');
-const d = dayjs(new Date(2023, 2, 23));
+d.toHijri();                              // { hy: 1444, hm: 9, hd: 1 }
-const hijri = d.toHijri();
+d.formatHijri('iD iMMMM iYYYY');         // '1 Ramadan 1444'
-// => { hy: 1444, hm: 9, hd: 1 }  (1 Ramadan 1444 AH)
+d.formatHijri('iYYYY-iMM-iDD');          // '1444-09-01'
 
-// Format using Hijri tokens mixed with standard Day.js tokens
+dayjs.fromHijri(1444, 10, 1).format('YYYY-MM-DD'); // '2023-04-21'
-d.formatHijri('iYYYY-iMM-iDD');        // => '1444-09-01'
-d.formatHijri('iD iMMMM iYYYY');       // => '1 Ramadan 1444'
-d.formatHijri('iD iMMMM iYYYY [at] HH:mm'); // => '1 Ramadan 1444 at 00:00'
-
-// Individual Hijri components
-d.hijriYear();   // => 1444
-d.hijriMonth();  // => 9
-d.hijriDay();    // => 1
-
-// Construct a Day.js instance from a Hijri date
-const eid = dayjs.fromHijri(1444, 10, 1);
-eid.format('YYYY-MM-DD'); // => '2023-04-21'
-
-// FCNA/ISNA calendar variant
-d.toHijri({ calendar: 'fcna' }); // => { hy: 1444, hm: 9, hd: 2 } (varies by month)
 ```
 
-## API
-
-### dayjs.extend(hijriPlugin)
-
-Register the plugin with your Day.js instance. Call once before using any plugin methods.
-
-### Instance Methods
-
-#### `.toHijri(opts?)`
-
-Convert the Day.js date to a Hijri date object.
-
-| Parameter | Type | Description |
-| --- | --- | --- |
-| `opts` | `ConversionOptions` | Optional. `{ calendar: 'uaq' \| 'fcna' \| string }` |
-
-Returns `HijriDate | null`. Returns `null` if the date is outside the supported range (UAQ: AH 1318-1500 / 1900-2076 CE).
-
-```ts
-dayjs('2023-03-23').toHijri();
-// => { hy: 1444, hm: 9, hd: 1 }
-```
-
-#### `.isValidHijri(opts?)`
-
-Check whether the date maps to a valid Hijri date in the supported range.
-
-Returns `boolean`.
-
-#### `.hijriYear(opts?)`
-
-Returns the Hijri year as a `number`, or `null` if out of range.
-
-#### `.hijriMonth(opts?)`
-
-Returns the Hijri month (1-12) as a `number`, or `null` if out of range.
-
-#### `.hijriDay(opts?)`
-
-Returns the Hijri day (1-30) as a `number`, or `null` if out of range.
-
-#### `.formatHijri(formatStr, opts?)`
-
-Format the date using a mix of Hijri tokens and standard Day.js tokens.
-
-| Parameter | Type | Description |
-| --- | --- | --- |
-| `formatStr` | `string` | Format string. See token table below. |
-| `opts` | `ConversionOptions` | Optional calendar selection |
-
-Returns `string`. Returns an empty string if the date is out of range.
-
-Hijri tokens are replaced first. The resulting string is then passed to Day.js `.format()`, so all standard tokens (YYYY, MM, DD, HH, mm, ss, etc.) resolve normally.
-
-### Static Methods
-
-#### `dayjs.fromHijri(hy, hm, hd, opts?)`
-
-Construct a Day.js instance from a Hijri date.
-
-| Parameter | Type | Description |
-| --- | --- | --- |
-| `hy` | `number` | Hijri year |
-| `hm` | `number` | Hijri month (1-12) |
-| `hd` | `number` | Hijri day (1-30) |
-| `opts` | `ConversionOptions` | Optional calendar selection |
-
-Returns a `dayjs.Dayjs` instance. Throws `Error` if the Hijri date is invalid or outside the table range.
-
-## Format Tokens
-
-All Hijri-specific tokens use the `i` prefix.
-
-| Token | Example | Description |
-| --- | --- | --- |
-| `iYYYY` | `1444` | 4-digit Hijri year |
-| `iYY` | `44` | 2-digit Hijri year |
-| `iMMMM` | `Ramadan` | Full Hijri month name |
-| `iMMM` | `Ramadan` | Medium Hijri month name |
-| `iMM` | `09` | Zero-padded Hijri month number |
-| `iM` | `9` | Hijri month number |
-| `iDD` | `01` | Zero-padded Hijri day |
-| `iD` | `1` | Hijri day number |
-| `iEEEE` | `Yawm al-Khamis` | Full weekday name |
-| `iEEE` | `Kham` | Short weekday name |
-| `iE` | `5` | Weekday number (1=Sunday ... 7=Saturday) |
-| `ioooo` | `AH` | Era (Anno Hegirae) |
-| `iooo` | `AH` | Era (short form, same as ioooo) |
-
-Standard Day.js tokens pass through untouched. Square-bracket escaping (`[literal text]`) also works as expected.
-
-## Calendar Systems
-
-Two calendars ship with hijri-core:
-
-- **`uaq`** (default): Umm al-Qura, the official calendar of Saudi Arabia. Table-based, covers 1318-1500 AH (1900-2076 CE).
-- **`fcna`**: Fiqh Council of North America calendar. Uses an astronomical calculation with fixed criteria, independent of moon sighting.
-
-Select a calendar by passing `{ calendar: 'fcna' }` to any method. The default is `'uaq'` when no option is provided.
-
-Custom calendar engines can be registered:
-
-```ts
-import { registerCalendar } from 'dayjs-hijri-plus';
-import type { CalendarEngine } from 'dayjs-hijri-plus';
-
-const myEngine: CalendarEngine = { ... };
-registerCalendar('my-calendar', myEngine);
-
-dayjs().toHijri({ calendar: 'my-calendar' });
-```
-
-See the [hijri-core CalendarEngine interface](https://github.com/acamarata/hijri-core) for the full contract.
-
-## TypeScript
-
-Full TypeScript support is included. The plugin augments the Day.js module to add types for all instance and static methods.
-
-```ts
-import type { HijriDate, ConversionOptions } from 'dayjs-hijri-plus';
-
-const h: HijriDate = dayjs().toHijri()!;
-const opts: ConversionOptions = { calendar: 'fcna' };
-```
-
-No `@types` package is needed.
-
-## Architecture
-
-A thin plugin wrapper over [hijri-core](https://github.com/acamarata/hijri-core). The plugin augments the Day.js prototype with Hijri methods, each delegating to the registered calendar engine. Zero global state: calendar selection is passed per call.
-
-For more detail see the [Architecture wiki page](https://github.com/acamarata/dayjs-hijri-plus/wiki/Architecture).
-
 ## Documentation
 
-Full API reference, architecture notes, and calendar system comparisons are on the [GitHub Wiki](https://github.com/acamarata/dayjs-hijri-plus/wiki).
+Full API reference, examples, and architecture notes are on the [GitHub Wiki](https://github.com/acamarata/dayjs-hijri-plus/wiki).
+
+## Day boundaries and time zones
+
+`.toHijri()` converts the calendar date the dayjs instance displays — the same date you would read off the screen — regardless of the host's system timezone or whether the dayjs `utc` plugin is active. A call like `dayjs('2025-03-01').toHijri()` always maps the 1st of March 2025, not whatever local instant that string resolves to in UTC.
+
+Religious start-of-day at sunset is out of scope. Sunset-aware day boundaries require external prayer-time data and are not handled here.
 
 ## Related
 
-- [hijri-core](https://github.com/acamarata/hijri-core): zero-dependency Hijri calendar engine this plugin wraps
+- [hijri-core](https://github.com/acamarata/hijri-core): the zero-dependency Hijri calendar engine this plugin wraps
-- [luxon-hijri](https://github.com/acamarata/luxon-hijri): the same Hijri conversion for Luxon users
+- [luxon-hijri](https://github.com/acamarata/luxon-hijri): the same conversion for Luxon users
 - [pray-calc](https://github.com/acamarata/pray-calc): Islamic prayer time calculation
-- [nrel-spa](https://github.com/acamarata/nrel-spa): NREL Solar Position Algorithm in pure JavaScript
-
-## Compatibility
-
-- Node.js 20, 22, 24
-- Day.js 1.x (peer dependency)
-- ESM and CJS builds included
-- TypeScript definitions bundled
-
-## Acknowledgments
-
-Calendar data and algorithms provided by [hijri-core](https://github.com/acamarata/hijri-core). The Umm al-Qura table is derived from data published by the King Abdulaziz City for Science and Technology (KACST). FCNA new moon calculations follow Jean Meeus, "Astronomical Algorithms," 2nd ed., Chapter 49.
 
 ## License
 

eslint.config.mjs

@@ -1,12 +1,20 @@
-import eslint from '@eslint/js';
+import tsParser from '@typescript-eslint/parser';
-import tseslint from 'typescript-eslint';
+import tsPlugin from '@typescript-eslint/eslint-plugin';
 import eslintConfigPrettier from 'eslint-config-prettier';
+import { typescript } from '@acamarata/eslint-config';
 
-export default tseslint.config(
+export default [
-  eslint.configs.recommended,
+  {
-  ...tseslint.configs.recommended,
+    files: ['**/*.ts', '**/*.tsx'],
+    plugins: { '@typescript-eslint': tsPlugin },
+    languageOptions: {
+      parser: tsParser,
+      parserOptions: { project: true, tsconfigRootDir: import.meta.dirname },
+    },
+  },
+  ...typescript.map((cfg) => ({ ...cfg, files: ['**/*.ts', '**/*.tsx'] })),
   eslintConfigPrettier,
   {
     ignores: ['dist/', 'node_modules/', 'test.mjs', 'test-cjs.cjs'],
   },
-);
+];

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dayjs-hijri-plus",
-  "version": "1.0.1",
+  "version": "1.0.4",
   "description": "Day.js plugin for Hijri calendar conversion and formatting. Supports Umm al-Qura and FCNA calendars via hijri-core.",
   "author": "Aric Camarata",
   "license": "MIT",
@@ -37,8 +37,10 @@
     "lint": "eslint src/",
     "format": "prettier --write src/",
     "format:check": "prettier --check src/",
-    "prepublishOnly": "tsup",
+    "prepack": "pnpm run build",
-    "coverage": "c8 --reporter=lcov --reporter=text node --test"
+    "coverage": "c8 --reporter=lcov --reporter=text node test.mjs",
+    "docs": "typedoc --out .github/wiki/api src/index.ts",
+    "postbuild": "cp dist/index.d.ts dist/index.d.mts"
   },
   "keywords": [
     "dayjs",
@@ -57,14 +59,22 @@
     "hijri-core": "^1.0.0"
   },
   "devDependencies": {
+    "@acamarata/eslint-config": "^0.1.0",
+    "@acamarata/prettier-config": "^0.1.0",
+    "@acamarata/tsconfig": "^0.1.0",
     "@eslint/js": "^10.0.1",
     "@types/node": "^25.3.5",
+    "@typescript-eslint/eslint-plugin": "^8.56.1",
+    "@typescript-eslint/parser": "^8.56.1",
+    "c8": "^10.1.3",
     "dayjs": "^1.11.0",
     "eslint": "^10.0.3",
     "eslint-config-prettier": "^10.1.8",
-    "hijri-core": "^1.0.0",
+    "hijri-core": "^1.0.3",
     "prettier": "^3.8.1",
     "tsup": "^8.0.0",
+    "typedoc": "^0.28.19",
+    "typedoc-plugin-markdown": "^4.11.0",
     "typescript": "^5.5.0",
     "typescript-eslint": "^8.56.1"
   },
@@ -80,5 +90,6 @@
   "bugs": {
     "url": "https://github.com/acamarata/dayjs-hijri-plus/issues"
   },
-  "type": "module"
+  "type": "module",
+  "prettier": "@acamarata/prettier-config"
 }

src/index.ts

@@ -1,28 +1,87 @@
-import type { PluginFunc } from 'dayjs';
+import type { PluginFunc } from "dayjs";
-import { toHijri, toGregorian, hmLong, hmMedium, hwLong, hwShort, hwNumeric } from 'hijri-core';
+import { toHijri, toGregorian, hmLong, hmMedium, hwLong, hwShort, hwNumeric } from "hijri-core";
-import type { ConversionOptions, HijriDate } from './types';
+import type { ConversionOptions, HijriDate } from "./types";
 
 // Augment Day.js to expose plugin methods on the instance type.
-declare module 'dayjs' {
+declare module "dayjs" {
   interface Dayjs {
-    /** Convert to a Hijri date. Returns null if outside the supported range. */
+    /**
+     * Convert the Day.js date to a Hijri date.
+     *
+     * @param opts - Optional calendar selection. Defaults to `{ calendar: 'uaq' }`.
+     * @returns `{ hy, hm, hd }` on success, or `null` if the date is outside the
+     *   supported range (UAQ: 1318-1500 AH / approximately 1900-2076 CE).
+     * @example
+     * dayjs('2023-03-23').toHijri();
+     * // => { hy: 1444, hm: 9, hd: 1 }
+     */
     toHijri(opts?: ConversionOptions): HijriDate | null;
 
-    /** Check whether the date maps to a valid Hijri date in the supported range. */
+    /**
+     * Check whether the date maps to a valid Hijri date in the supported range.
+     *
+     * Equivalent to `d.toHijri(opts) !== null`.
+     *
+     * @param opts - Optional calendar selection.
+     * @returns `true` if the date is in range, `false` otherwise.
+     * @example
+     * dayjs('2023-03-23').isValidHijri(); // true
+     * dayjs('1800-01-01').isValidHijri(); // false
+     */
     isValidHijri(opts?: ConversionOptions): boolean;
 
-    /** Hijri year component, or null if out of range. */
+    /**
+     * Return the Hijri year of the date.
+     *
+     * @param opts - Optional calendar selection.
+     * @returns The Hijri year as a `number`, or `null` if out of range.
+     * @example
+     * dayjs('2023-03-23').hijriYear(); // 1444
+     */
     hijriYear(opts?: ConversionOptions): number | null;
 
-    /** Hijri month component (1-12), or null if out of range. */
+    /**
+     * Return the Hijri month (1-12) of the date.
+     *
+     * Month 1 = Muharram, month 9 = Ramadan, month 12 = Dhu al-Hijjah.
+     *
+     * @param opts - Optional calendar selection.
+     * @returns The Hijri month in the range 1-12, or `null` if out of range.
+     * @example
+     * dayjs('2023-03-23').hijriMonth(); // 9 (Ramadan)
+     */
     hijriMonth(opts?: ConversionOptions): number | null;
 
-    /** Hijri day component (1-30), or null if out of range. */
+    /**
+     * Return the Hijri day of month (1-30) of the date.
+     *
+     * @param opts - Optional calendar selection.
+     * @returns The Hijri day in the range 1-30, or `null` if out of range.
+     * @example
+     * dayjs('2023-03-23').hijriDay(); // 1
+     */
     hijriDay(opts?: ConversionOptions): number | null;
 
     /**
-     * Format the date using Hijri tokens (i-prefixed) and standard Day.js tokens.
+     * Format the date using a mix of Hijri tokens (`i`-prefixed) and standard
-     * Returns an empty string if the date is outside the supported range.
+     * Day.js tokens.
+     *
+     * Hijri tokens are replaced first. The resulting string is then passed to
+     * Day.js `.format()`, so all standard tokens (YYYY, MM, DD, HH, mm, ss, etc.)
+     * resolve normally.
+     *
+     * @param formatStr - Format string containing Hijri tokens, Day.js tokens, or both.
+     * @param opts - Optional calendar selection.
+     * @returns The formatted string, or an empty string if the date is out of range.
+     * @example
+     * dayjs('2023-03-23').formatHijri('iD iMMMM iYYYY');
+     * // => '1 Ramadan 1444'
+     *
+     * dayjs('2023-03-23').formatHijri('iYYYY-iMM-iDD');
+     * // => '1444-09-01'
+     *
+     * dayjs('2023-03-23').formatHijri('iD iMMMM iYYYY [at] HH:mm');
+     * // => '1 Ramadan 1444 at 00:00'
      */
     formatHijri(formatStr: string, opts?: ConversionOptions): string;
   }
@@ -32,13 +91,33 @@ declare module 'dayjs' {
 // Using the function declaration form (same pattern as dayjs timezone plugin)
 // because dayjs does not export an IStatic interface for module augmentation.
 // import('dayjs').Dayjs is used explicitly to satisfy the tsup DTS emitter.
-declare module 'dayjs' {
+declare module "dayjs" {
+  /**
+   * Construct a Day.js instance from a Hijri date.
+   *
+   * The result is built from an ISO date string (`YYYY-MM-DD`) to avoid
+   * UTC midnight converting to the previous local day in western timezones.
+   *
+   * @param hy - Hijri year.
+   * @param hm - Hijri month (1-12).
+   * @param hd - Hijri day (1-30).
+   * @param opts - Optional calendar selection. Defaults to `{ calendar: 'uaq' }`.
+   * @returns A `dayjs.Dayjs` instance at midnight local time on the corresponding
+   *   Gregorian date.
+   * @throws {Error} If the Hijri date is invalid or outside the table range.
+   * @example
+   * dayjs.fromHijri(1444, 9, 1).format('YYYY-MM-DD');
+   * // => '2023-03-23'
+   *
+   * dayjs.fromHijri(1444, 10, 1).format('YYYY-MM-DD');
+   * // => '2023-04-21'  (Eid al-Fitr 1444)
+   */
   function fromHijri(
     hy: number,
     hm: number,
     hd: number,
     opts?: ConversionOptions,
-  ): import('dayjs').Dayjs;
+  ): import("dayjs").Dayjs;
 }
 
 // Hijri-specific format tokens, ordered longest-first to prevent partial matches.
@@ -53,19 +132,46 @@ const HIJRI_TOKEN_RE = /iYYYY|iYY|iMMMM|iMMM|iMM|iM|iDD|iD|iEEEE|iEEE|iE|ioooo|i
  * Day.js uses `[...]` for literal text. A `]` inside such a section would
  * close it prematurely, so we split on `]` and re-join with `][` (which
  * closes the current literal section, outputs a raw `]` (Day.js passes
- * unrecognised characters through untouched), then opens a new one.
+ * unrecognised characters through untouched), then opens a new one).
+ *
+ * @param value - Plain string to escape.
+ * @returns The bracket-escaped string.
  */
 function lit(value: string): string {
-  return '[' + value.split(']').join(']][') + ']';
+  return "[" + value.split("]").join("]][") + "]";
 }
 
+/**
+ * Day.js plugin that adds Hijri calendar support.
+ *
+ * Register once with `dayjs.extend(hijriPlugin)`. After that, all `dayjs()`
+ * instances expose `.toHijri()`, `.isValidHijri()`, `.hijriYear()`,
+ * `.hijriMonth()`, `.hijriDay()`, and `.formatHijri()`. The static factory
+ * `dayjs.fromHijri(hy, hm, hd)` is also added.
+ *
+ * All calendar arithmetic is delegated to hijri-core. This plugin adds no
+ * conversion logic of its own.
+ *
+ * @example
+ * import dayjs from 'dayjs';
+ * import hijriPlugin from 'dayjs-hijri-plus';
+ *
+ * dayjs.extend(hijriPlugin);
+ *
+ * dayjs('2023-03-23').toHijri();
+ * // => { hy: 1444, hm: 9, hd: 1 }
+ */
 const plugin: PluginFunc = (_option, dayjsClass, dayjsFactory) => {
   // ------------------------------------------------------------------ //
   //  Instance methods                                                    //
   // ------------------------------------------------------------------ //
 
   dayjsClass.prototype.toHijri = function (opts?: ConversionOptions): HijriDate | null {
-    return toHijri(this.toDate(), opts);
+    // Build a UTC-noon Date from the calendar date this instance displays so
+    // that hijri-core's UTC-day contract reads the correct day regardless of
+    // the host timezone or whether the dayjs utc plugin is active.
+    // dayjs .month() is 0-based, matching Date.UTC's month parameter.
+    return toHijri(new Date(Date.UTC(this.year(), this.month(), this.date())), opts);
   };
 
   dayjsClass.prototype.isValidHijri = function (opts?: ConversionOptions): boolean {
@@ -89,7 +195,7 @@ const plugin: PluginFunc = (_option, dayjsClass, dayjsFactory) => {
     opts?: ConversionOptions,
   ): string {
     const hijri = this.toHijri(opts);
-    if (!hijri) return '';
+    if (!hijri) return "";
 
     // Day.js .day() returns 0 (Sunday) ... 6 (Saturday), matching the index
     // layout of hwLong, hwShort, and hwNumeric from hijri-core.
@@ -97,31 +203,38 @@ const plugin: PluginFunc = (_option, dayjsClass, dayjsFactory) => {
 
     const replaced = formatStr.replace(HIJRI_TOKEN_RE, (token) => {
       switch (token) {
-        case 'iYYYY':
+        case "iYYYY":
-          return lit(String(hijri.hy).padStart(4, '0'));
+          return lit(String(hijri.hy).padStart(4, "0"));
-        case 'iYY':
+        case "iYY":
-          return lit(String(hijri.hy % 100).padStart(2, '0'));
+          return lit(String(hijri.hy % 100).padStart(2, "0"));
-        case 'iMMMM':
+        case "iMMMM":
-          return lit(hmLong[hijri.hm - 1]);
+          // Non-null: hijri.hm is a valid Hijri month 1-12; hm-1 is always within hmLong bounds.
-        case 'iMMM':
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-          return lit(hmMedium[hijri.hm - 1]);
+          return lit(hmLong[hijri.hm - 1]!);
-        case 'iMM':
+        case "iMMM":
-          return lit(String(hijri.hm).padStart(2, '0'));
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-        case 'iM':
+          return lit(hmMedium[hijri.hm - 1]!);
+        case "iMM":
+          return lit(String(hijri.hm).padStart(2, "0"));
+        case "iM":
           return lit(String(hijri.hm));
-        case 'iDD':
+        case "iDD":
-          return lit(String(hijri.hd).padStart(2, '0'));
+          return lit(String(hijri.hd).padStart(2, "0"));
-        case 'iD':
+        case "iD":
           return lit(String(hijri.hd));
-        case 'iEEEE':
+        case "iEEEE":
-          return lit(hwLong[dow]);
+          // Non-null: dow is always 0-6 (day of week), within hwLong bounds.
-        case 'iEEE':
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-          return lit(hwShort[dow]);
+          return lit(hwLong[dow]!);
-        case 'iE':
+        case "iEEE":
-          return lit(String(hwNumeric[dow]));
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-        case 'ioooo':
+          return lit(hwShort[dow]!);
-        case 'iooo':
+        case "iE":
-          return lit('AH');
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          return lit(String(hwNumeric[dow]!));
+        case "ioooo":
+        case "iooo":
+          return lit("AH");
         default:
           return token;
       }
@@ -153,22 +266,40 @@ const plugin: PluginFunc = (_option, dayjsClass, dayjsFactory) => {
     if (!greg) {
       throw new Error(`Invalid or out-of-range Hijri date: ${hy}/${hm}/${hd}`);
     }
-    // Construct from ISO date string to avoid timezone offset issues.
+    // Construct from an ISO date string (YYYY-MM-DD) so the result is the
-    // dayjsFactory(Date) interprets the Date in local time; a UTC-midnight Date
+    // Gregorian calendar day that corresponds to the Hijri date, at local
-    // in western timezones would resolve to the previous local day.
+    // midnight in whatever timezone the consumer uses. Passing a raw Date
+    // object to dayjsFactory() would interpret it as a UTC instant and could
+    // land on the previous local day for hosts west of UTC.
     const y = greg.getUTCFullYear();
-    const mo = String(greg.getUTCMonth() + 1).padStart(2, '0');
+    const mo = String(greg.getUTCMonth() + 1).padStart(2, "0");
-    const dy = String(greg.getUTCDate()).padStart(2, '0');
+    const dy = String(greg.getUTCDate()).padStart(2, "0");
     return dayjsFactory(`${y}-${mo}-${dy}`);
   };
 };
 
 export default plugin;
 
-// Re-export hijri-core types for consumers who import from dayjs-hijri-plus.
+/**
-export type { HijriDate, ConversionOptions } from './types';
+ * Re-exported from hijri-core for consumers who import from dayjs-hijri-plus.
-export type { CalendarEngine } from 'hijri-core';
+ * Avoids requiring hijri-core as a direct dependency just to use these types.
+ */
+export type { HijriDate, ConversionOptions } from "./types";
 
-// Re-export the registry API so callers can register custom calendar engines
+/**
-// without adding hijri-core as a direct dependency.
+ * Re-exported CalendarEngine interface from hijri-core.
-export { registerCalendar, getCalendar, listCalendars } from 'hijri-core';
+ * Use this type to implement custom calendar engines for `registerCalendar`.
+ */
+export type { CalendarEngine } from "hijri-core";
+
+/**
+ * Re-exported registry API from hijri-core.
+ * Register, retrieve, or list custom calendar engines without adding
+ * hijri-core as a direct dependency.
+ *
+ * @example
+ * import { registerCalendar, listCalendars } from 'dayjs-hijri-plus';
+ * registerCalendar('my-cal', myEngine);
+ * listCalendars(); // ['uaq', 'fcna', 'my-cal']
+ */
+export { registerCalendar, getCalendar, listCalendars } from "hijri-core";

src/types.ts

@@ -1,2 +1,2 @@
-import type { HijriDate, ConversionOptions } from 'hijri-core';
+import type { HijriDate, ConversionOptions } from "hijri-core";
 export type { HijriDate, ConversionOptions };

test-cjs.cjs

@@ -59,3 +59,16 @@ describe('CJS: isValidHijri', () => {
     assert.equal(dayjs(D_RAMADAN_1444).isValidHijri(), true);
   });
 });
+
+describe('CJS: UTC-day boundary (regression)', () => {
+  it('dayjs("2025-03-01").toHijri() -> 1 Ramadan 1446', () => {
+    const h = dayjs('2025-03-01').toHijri();
+    assert.deepEqual(h, { hy: 1446, hm: 9, hd: 1 });
+  });
+
+  it('round-trip: fromHijri(1446,9,1) then toHijri() -> {1446,9,1}', () => {
+    const d = dayjs.fromHijri(1446, 9, 1);
+    const h = d.toHijri();
+    assert.deepEqual(h, { hy: 1446, hm: 9, hd: 1 });
+  });
+});

test.mjs

@@ -102,3 +102,18 @@ describe('isValidHijri', () => {
     assert.equal(valid, true);
   });
 });
+
+describe('UTC-day boundary (regression)', () => {
+  // dayjs("YYYY-MM-DD") parses as local midnight — timezone-invariant anchor
+  // for toHijri now that the adapter reads the displayed calendar date.
+  it('dayjs("2025-03-01").toHijri() -> 1 Ramadan 1446', () => {
+    const h = dayjs('2025-03-01').toHijri();
+    assert.deepEqual(h, { hy: 1446, hm: 9, hd: 1 });
+  });
+
+  it('round-trip: fromHijri(1446,9,1) then toHijri() -> {1446,9,1}', () => {
+    const d = dayjs.fromHijri(1446, 9, 1);
+    const h = d.toHijri();
+    assert.deepEqual(h, { hy: 1446, hm: 9, hd: 1 });
+  });
+});

tsconfig.json

@@ -1,17 +1,9 @@
 {
+  "extends": "@acamarata/tsconfig/tsconfig.library.json",
   "compilerOptions": {
-    "target": "ES2020",
-    "module": "ESNext",
-    "moduleResolution": "bundler",
-    "strict": true,
-    "forceConsistentCasingInFileNames": true,
-    "esModuleInterop": true,
-    "declaration": true,
-    "declarationMap": true,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
-    "sourceMap": true,
+    "esModuleInterop": true,
-    "outDir": "dist",
     "rootDir": "src",
     "types": ["node"]
   },

typedoc.json

@@ -0,0 +1,10 @@
+{
+  "entryPoints": ["src/index.ts"],
+  "out": ".github/wiki/api",
+  "plugin": ["typedoc-plugin-markdown"],
+  "readme": "none",
+  "skipErrorChecking": false,
+  "excludePrivate": true,
+  "excludeProtected": true,
+  "includeVersion": true
+}