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TS I18n

@productdevbook/ts-i18n

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"ts-i18n" is a Typescript library that facilitates internationalization (i18n) in both browser and ES module environments (Node). It offers a lightweight solution for interpolation and pluralization.

Unlike some i18n libraries, ts-i18n doesn't handle the actual translation of phrases. Instead, it provides tools for managing translated phrases within your client or server-side Typescript application, making it agnostic to the translation backend used."

Features

  • Typescript support
  • Node.js Version >= 18.0.0
  • ES module support
  • Type Safe and Auto Complete
  • Unplugin TS Safe

Sponsors

sponsors

Installation

pnpm add @productdevbook/ts-i18n

Usage

Translation

Tell Polyglot what to say by simply giving it a phrases object, where the key is the canonical name of the phrase and the value is the already-translated string.

import { Polyglot } from '@productdevbook/ts-i18n'

const polyglot = new Polyglot({
  locale: 'en',
})

polyglot.extend({
  hello: 'Hello'
})

polyglot.t('hello') // Hello

You can also pass a mapping at instantiation, using the key phrases:

const polyglot = new Polyglot({ phrases: { hello: 'Hello' } })

Polyglot doesn’t do the translation for you. It’s up to you to give it the proper phrases for the user’s locale.

Type Safety - Unplugin

This structure allows you to convert a given json file to TS and creates the interface for ts-i18n. The resulting file then needs to be imported instead of new Polyglot<T> T.

Vite
// vite.config.ts
import TSI18n from '@productdevbook/ts-i18n/vite'

export default defineConfig({
  plugins: [
    TSI18n({
      exportFilePath: './i18n.d.ts',
      localesFolder: 'locales',
      selectLanguage: 'en',
    }),
  ],
})


Webpack
// webpack.config.ts
module.exports = {
  /* ... */
  plugins: [
    require('@productdevbook/ts-i18n/webpack')({
      exportFilePath: './i18n.d.ts',
      localesFolder: 'locales',
      selectLanguage: 'en',
    }),
  ],
}


Rollup
// rollup.config.js
import TSI18n from '@productdevbook/ts-i18n/rollup'

export default {
  plugins: [
    TSI18n({
      exportFilePath: './i18n.d.ts',
      localesFolder: 'locales',
      selectLanguage: 'en',
    }),
  ],
}


ESBuild
// esbuild.config.js
// esbuild.config.js
import { build } from 'esbuild'

build({
  /* ... */
  plugins: [
    require('@productdevbook/ts-i18n/esbuild')({
      exportFilePath: './i18n.d.ts',
      localesFolder: 'locales',
      selectLanguage: 'en',
    }),
  ],
})


Nuxt

You might not need this plugin for Nuxt. Use @productdevbook/ts-i18n/nuxt instead.

// nuxt.config.ts

export default defineNuxtConfig({
  modules: [
    '@productdevbook/ts-i18n/nuxt',
  ],

  tsI18n: {
    exportFilePath: './i18n.d.ts',
    localesFolder: 'locales',
    selectLanguage: 'en',
  },
})


Locale Files

If you tell it which folder the language files are in, it will automatically fetch the language according to that locale and get the values from it.

import { Polyglot } from '@productdevbook/ts-i18n'
import type { I18nTranslations } from './i18n'

const i18n = new Polyglot<I18nTranslations>({
  locale: 'en',
  loaderOptions: {
    path: 'locales',
  },
})

i18n.t('hello') // Hello

const i18n = new Polyglot<I18nTranslations>({
  locale: 'tr',
  loaderOptions: {
    path: 'locales',
  },
})

i18n.t('hello') // Merhaba

Error Missing Translation

If you want to throw an error when a translation is missing, you can use the errorOnMissing option.

const i18n = new Polyglot({
  errorOnMissing: true,
})

Interpolation

Polyglot.t() also provides interpolation. Pass an object with key-value pairs of interpolation arguments as the second parameter.

import { Polyglot } from '@productdevbook/ts-i18n'

const polyglot = new Polyglot({
  locale: 'en',
  phrases: {
    hello_name: 'Hello %{name}',
  },
})

polyglot.extend({
  hello_name: 'Hola, %{name}.'
})

polyglot.t('hello_name', { name: 'DeNiro' }) // Hola, DeNiro.

Polyglot also supports nested phrase objects.

polyglot.extend({
  nav: {
    hello: 'Hello',
    hello_name: 'Hello, %{name}',
    sidebar: {
      welcome: 'Welcome'
    }
  }
})

polyglot.t('nav.sidebar.welcome') // Welcome

The substitution variable syntax is customizable.

const polyglot = new Polyglot({
  locale: 'en',
  phrases: {
    hello_name: 'Hola {{name}}'
  },
  interpolation: { prefix: '{{', suffix: '}}' }
})

polyglot.t('hello_name', { name: 'DeNiro' }) // Hola DeNiro

Pluralization

For pluralization to work properly, you need to tell Polyglot what the current locale is. You can use polyglot.locale("tr") to set the locale to, for example, Turkish. This method is also a getter:

polyglot.locale() // tr

You can also pass this in during instantiation.

const polyglot = new Polyglot({ locale: 'tr' })

Currently, the only thing that Polyglot uses this locale setting for is pluralization.

Polyglot provides a very basic pattern for providing pluralization based on a single string that contains all plural forms for a given phrase. Because various languages have different nominal forms for zero, one, and multiple, and because the noun can be before or after the count, we have to be overly explicit about the possible phrases.

To get a pluralized phrase, still use polyglot.t() but use a specially-formatted phrase string that separates the plural forms by the delimiter ||||, or four vertical pipe characters.

For pluralizing "car" in English, Polyglot assumes you have a phrase of the form:

polyglot.extend({
  num_cars: '%{smart_count} car |||| %{smart_count} cars',
})

Please keep in mind that smart_count is required. No other option name is taken into account to transform pluralization strings.

In English (and German, Spanish, Italian, and a few others) there are only two plural forms: singular and not-singular.

Some languages get a bit more complicated. In Czech, there are three separate forms: 1, 2 through 4, and 5 and up. Russian is even more involved.

const polyglot = new Polyglot({ locale: 'cs' }) // Czech
polyglot.extend({
  num_foxes: 'Mám %{smart_count} lišku |||| Mám %{smart_count} lišky |||| Mám %{smart_count} lišek'
})

polyglot.t() will choose the appropriate phrase based on the provided smart_count option, whose value is a number.

polyglot.t('num_cars', { smart_count: 0 }) // 0 cars

polyglot.t('num_cars', { smart_count: 1 }) // 1 car

polyglot.t('num_cars', { smart_count: 2 }) // 2 cars

As a shortcut, you can also pass a number to the second parameter:

polyglot.t('num_cars', 2) // 2 cars

Custom Pluralization Rules

Polyglot provides some default pluralization rules for some locales. You can specify a different set of rules through the pluralRules constructor param.

const polyglot = new Polyglot({
  locale: 'en',
  pluralRules: {
    pluralTypes: {
      germanLike(n) {
        // is 1
        if (n === 1)
          return 0

        // everything else
        return 1
      },
      frenchLike(n) {
        // is 0 or 1
        if (n <= 1)
          return 0

        // everything else
        return 1
      }
    },
    pluralTypeToLanguages: {
      germanLike: ['de', 'en', 'xh', 'zu'],
      frenchLike: ['fr', 'hy']
    }
  }
})

This can be useful to support locales that polyglot does not support by default or to change the rule definitions.

Public Instance Methods

Polyglot.t(key, interpolationOptions)

The most-used method. Provide a key, and t() will return the phrase.

polyglot.t('hello') // Hello

The phrase value is provided first by a call to polyglot.extend() or polyglot.replace().

Pass in an object as the second argument to perform interpolation.

polyglot.t('hello_name', { name: 'Spike' }) // Hello, Spike.

Pass a number as the second argument as a shortcut to smart_count:

// same as: polyglot.t("car", {smart_count: 2});
polyglot.t('car', 2) // 2 cars

If you like, you can provide a default value in case the phrase is missing. Use the special option key "_" to specify a default.

polyglot.t('i_like_to_write_in_language', {
  _: 'I like to write in %{language}.',
  language: 'JavaScript'
}) // I like to write in JavaScript.

Polyglot.extend(phrases)

Use extend to tell Polyglot how to translate a given key.

polyglot.extend({
  hello: 'Hello',
  hello_name: 'Hello, %{name}'
})

The key can be any string. Feel free to call extend multiple times; it will override any phrases with the same key, but leave existing phrases untouched.

Polyglot.unset(keyOrObject)

Use unset to selectively remove keys from a polyglot instance. unset accepts one argument: either a single string key, or an object whose keys are string keys, and whose values are ignored unless they are nested objects (in the same format).

Example:

polyglot.unset('some_key')
polyglot.unset({
  hello: 'Hello',
  hello_name: 'Hello, %{name}',
  foo: {
    bar: 'This phrase’s key is "foo.bar"'
  }
})

Polyglot.locale([localeToSet])

Get or set the locale (also can be set using the constructor option, which is used only for pluralization. If a truthy value is provided, it will set the locale. Afterwards, it will return it.

Polyglot.clear()

Clears all phrases. Useful for special cases, such as freeing up memory if you have lots of phrases but no longer need to perform any translation. Also used internally by replace.

Polyglot.replace(phrases)

Completely replace the existing phrases with a new set of phrases. Normally, just use extend to add more phrases, but under certain circumstances, you may want to make sure no old phrases are lying around.

Polyglot.has(key)

Returns true if the key does exist in the provided phrases, otherwise it will return false.

Public Static Methods

transformPhrase(phrase[, substitutions[, locale]])

Takes a phrase string and transforms it by choosing the correct plural form and interpolating it. This method is used internally by t. The correct plural form is selected if substitutions.smart_count is set. You can pass in a number instead of an Object as substitutions as a shortcut for smart_count. You should pass in a third argument, the locale, to specify the correct plural type. It defaults to 'en' which has 2 plural forms.

Development

  1. Run pnpm install to install the dependencies.
  2. Run pnpm dev to start the bundle.
  3. Run pnpm lint to lint the code. (You can also run pnpm lint:fix to fix the linting errors.)
  4. Run pnpm test to run the tests. (You can also run pnpm test:watch to run the tests in watch mode.)

TODO

  • Add more tests
  • Add more documentation
  • Add more examples
  • Path auto language files import

Source

The project will continue by translating TS from airbnb polyglot.js codes and adding additional features. The codes in some places have changed. Thank you airbnb. ❤️

Thanks

  • Type safety is inspired by nestjs-i18n. Thank you @toonvanstrijp. ❤️

License

This project is licensed under the MIT License.

productdevbook team