koa-locales

A modern i18n solution for Koa: @to-kn/koa-locales

Now TypeScript-first, ESM, and Node.js 18+!

• Uses ESM (import/export), outputs to dist/esm/, and is CI-tested on GitHub Actions.
• Use the built output (dist/esm/index.js) as the main entry point for consumers, but tests and development use the source (src/).
• Modern test suite with Vitest.

[![NPM version][npm-image]][npm-url]

koa locales, i18n solution for koa:

1. All locales resources location on options.dirs.
2. resources file supports: *.js, *.json, *.yml, *.yaml and *.properties, see examples.
3. One api: __(key[, value, ...]).
4. Auto detect request locale from query, cookie and header: Accept-Language.

Requirements

• Node.js >= 18
• ESM ("type": "module" in package.json)
• TypeScript (for development)

Installation

npm install @to-kn/koa-locales

Quick start (ESM/TypeScript)

import locales from '@to-kn/koa-locales';
import Koa from 'koa';

const app = new Koa();
const options = {
  dirs: [__dirname + '/locales', __dirname + '/foo/locales'],
};
locales(app, options);

Development & Testing

• Run tests with Vitest:

  npm run test

• Lint and format with Biome:

  npm run lint

• Build TypeScript to ESM:

  npm run build

• CI runs on GitHub Actions (see .github/workflows/)

API Reference

locales(app, options)

Patch locales functions to koa app.

• {Application} app: koa app instance.
• {Object} options: optional params.
  • {String} functionName: locale function name patch on koa context. Optional, default is __.
  • {String} dirs: locales resources store directories. Optional, default is ['$PWD/locales'].
  • {String} defaultLocale: default locale. Optional, default is en-US.
  • {String} queryField: locale field name on query. Optional, default is locale.
  • {String} cookieField: locale field name on cookie. Optional, default is locale.
  • {String} cookieDomain: domain on cookie. Optional, default is ''.
  • {Object} localeAlias: locale value map. Optional, default is {}.
  • {Boolean} writeCookie: set cookie if header not sent. Optional, default is true.
  • {String|Number} cookieMaxAge: set locale cookie value max age. Optional, default is 1y, expired after one year.

locales({
  app: app,
  dirs: [__dirname + '/app/locales'],
  defaultLocale: 'zh-CN',
});

Aliases

The key options.localeAlias allows to not repeat dictionary files, as you can configure to use the same file for es_ES for es, or en_UK for en.

locales({
  localeAlias: {
    es: es_ES,
    en: en_UK,
  },
});

context.__(key[, value1[, value2, ...]])

Get current request locale text.

async function home(ctx) {
  ctx.body = {
    message: ctx.__('Hello, %s', 'fengmk2'),
  };
}

Examples:

__('Hello, %s. %s', 'fengmk2', 'koa rock!')
=>
'Hello fengmk2. koa rock!'

__('{0} {0} {1} {1} {1}', ['foo', 'bar'])
=>
'foo foo bar bar bar'

__('{a} {a} {b} {b} {b}', {a: 'foo', b: 'bar'})
=>
'foo foo bar bar bar'

context.__getLocale()

Get locale from query / cookie and header.

context.__setLocale()

Set locale and cookie.

context.__getLocaleOrigin()

Where does locale come from, could be query, cookie, header and default.

app.__(locale, key[, value1[, value2, ...]])

Get the given locale text on application level.

console.log(app.__('zh', 'Hello'));
// stdout '你好' for Chinese

Usage on template

this.state.__ = this.__.bind(this);

[Nunjucks] example:

{{ __('Hello, %s', user.name) }}

[Pug] example:

p= __('Hello, %s', user.name)

[Koa-pug] integration:

You can set the property locals on the KoaPug instance, where the default locals are stored.

app.use(async (ctx, next) => {
  koaPug.locals.__ = ctx.__.bind(ctx);
  await next();
});

Debugging

If you are interested on knowing what locale was chosen and why you can enable the debug messages from [debug].

There is two level of verbosity:

$ DEBUG=koa-locales node .

With this line it only will show one line per request, with the chosen language and the origin where the locale come from (queryString, header or cookie).

$ DEBUG=koa-locales:silly node .

Locale File Formats

You can provide locale files in the following formats:

• .json (recommended for most use cases)
• .yml or .yaml
• .properties
• .cjs (CommonJS JavaScript, e.g. module.exports = { ... })

Note: .js ESM modules are not supported for synchronous loading. Use .cjs for JavaScript locale files if you need sync loading.