Architecture

Design goals

The package has one job: adapt the hijri-core API to Moment.js idioms. No calendar logic belongs here. All date arithmetic, table lookups, and validation live in hijri-core, which is tested and maintained independently.

This constraint keeps moment-hijri-plus small, maintainable, and calendar-agnostic. It benefits automatically from any calendar or correctness improvements made in hijri-core.

Plugin pattern

Moment.js plugins work by mutating moment.fn (the prototype for all moment instances) and the moment constructor itself. The canonical pattern is a single install(momentInstance) function that the caller invokes once:

import installHijri from 'moment-hijri-plus';
installHijri(moment);

This approach avoids accidental double-registration, keeps the plugin stateless, and works with any moment instance, including custom ones created by moment.utc() or locale-scoped instances.

Module augmentation

The TypeScript types are added to moment.Moment and moment.MomentStatic via declaration merging:

declare module 'moment' {
  interface MomentStatic {
    fromHijri(hy: number, hm: number, hd: number, options?: ConversionOptions): Moment;
  }
  interface Moment {
    toHijri(options?: ConversionOptions): HijriDate | null;
    // ...
  }
}

The augmentation is emitted in the declaration files produced by tsup, so consumers get full type inference without extra imports.

Format token system

formatHijri() uses a single regex pass to identify Hijri tokens, replaces them with resolved strings, then passes the residual format string to moment.format(). This means Gregorian tokens (YYYY, MMM, dddd, etc.) resolve exactly as they would without the plugin.

The regex is ordered longest-match-first to prevent prefix collisions:

/iYYYY|iYY|iMMMM|iMMM|iMM|iM|iDD|iD|iEEEE|iEEE|iE|ioooo|iooo/g;

iYYYY must appear before iYY for obvious reasons; iMMMM before iMMM and iMM; iDD before iD; iEEEE before iEEE. The global flag allows the regex to find all non-overlapping tokens in one pass.

Moment's own bracket escaping ([literal text]) is preserved because it only runs during the moment.format() call on the residual string. Any [...] sequences in the user's format string that don't contain Hijri tokens pass through untouched.

Delegation to hijri-core

Every conversion call goes through hijri-core:

toHijri()    →  hijri-core.toHijri(date, options)
fromHijri()  →  hijri-core.toGregorian(hy, hm, hd, options)

hijri-core maintains a registry of calendar engines. The default engine is uaq (Umm al-Qura). Callers can switch to fcna (FCNA/ISNA) or register custom engines via hijri-core's registerCalendar().

Because moment-hijri-plus uses hijri-core as a peer dependency, the registry is shared. A calendar registered in application code via hijri-core's registerCalendar() is immediately available to this plugin.

Build output

tsup produces four files:

File	Format	Purpose
`dist/index.cjs`	CommonJS	`require()` in Node.js and bundlers in CJS mode
`dist/index.mjs`	ESM	`import` in Node.js, Vite, Rollup, esbuild
`dist/index.d.ts`	CJS declaration	Types for CJS consumers (`require`)
`dist/index.d.mts`	ESM declaration	Types for ESM consumers (`import`)

Both moment and hijri-core are marked external, so they are not bundled. They resolve from the consumer's node_modules at runtime.

Calendar coverage

Calendar	ID	Range	Authority
Umm al-Qura	`uaq`	AH 1318-1500 (approx CE 1900-2076)	Official Saudi calendar
FCNA/ISNA	`fcna`	Calculated, no hard range	Fiqh Council of North America

The UAQ calendar is tabular: dates are looked up in a precomputed table published by the Umm al-Qura University. Dates outside the table return null. The FCNA calendar uses an astronomical calculation rule and has no strict boundary.

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