Introduction

This is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno.

Getting started

# npm package
$ npm install i18next-http-middleware

wire up i18next to request object

var i18next = require('i18next')
var middleware = require('i18next-http-middleware')
var express = require('express')

i18next.use(middleware.LanguageDetector).init({
  preload: ['en', 'de', 'it'],
  ...otherOptions
})

var app = express()
app.use(
  middleware.handle(i18next, {
    ignoreRoutes: ['/foo'] // or function(req, res, options, i18next) { /* return true to ignore */ }
  })
)

// in your request handler
app.get('myRoute', (req, res) => {
  var lng = req.language // 'de-CH'
  var lngs = req.languages // ['de-CH', 'de', 'en']
  req.i18n.changeLanguage('en') // will not load that!!! assert it was preloaded

  var exists = req.i18n.exists('myKey')
  var translation = req.t('myKey')
})

// in your views, eg. in pug (ex. jade)
div = t('myKey')

fastify usage

var i18next = require('i18next')
var middleware = require('i18next-http-middleware')
var fastify = require('fastify')

i18next.use(middleware.LanguageDetector).init({
  preload: ['en', 'de', 'it'],
  ...otherOptions
})

var app = fastify()
app.register(i18nextMiddleware.plugin, {
  i18next,
  ignoreRoutes: ['/foo'] // or function(req, res, options, i18next) { /* return true to ignore */ }
})
// or
// app.addHook('preHandler', i18nextMiddleware.handle(i18next, {
//   ignoreRoutes: ['/foo'] // or function(req, res, options, i18next) { /* return true to ignore */ }
// }))

// in your request handler
app.get('myRoute', (request, reply) => {
  var lng = request.language // 'de-CH'
  var lngs = v.languages // ['de-CH', 'de', 'en']
  request.i18n.changeLanguage('en') // will not load that!!! assert it was preloaded

  var exists = request.i18n.exists('myKey')
  var translation = request.t('myKey')
})

add routes

// missing keys make sure the body is parsed (i.e. with [body-parser](https://github.com/expressjs/body-parser#bodyparserjsonoptions))
app.post('/locales/add/:lng/:ns', middleware.missingKeyHandler(i18next))

// multiload backend route
app.get('/locales/resources.json', middleware.getResourcesHandler(i18next))

add localized routes

You can add your routes directly to the express app

var express = require('express'),
  app = express(),
  i18next = require('i18next'),
  FilesystemBackend = require('i18next-fs-backend'),
  i18nextMiddleware = require('i18next-http-middleware'),
  port = 3000

i18next
  .use(i18nextMiddleware.LanguageDetector)
  .use(FilesystemBackend)
  .init({ preload: ['en', 'de', 'it'], ...otherOptions }, () => {
    i18nextMiddleware.addRoute(
      i18next,
      '/:lng/key-to-translate',
      ['en', 'de', 'it'],
      app,
      'get',
      (req, res) => {
        //endpoint function
      }
    )
  })
app.use(i18nextMiddleware.handle(i18next))
app.listen(port, () => {
  console.log('Server listening on port', port)
})

or to an express router

var express = require('express'),
  app = express(),
  i18next = require('i18next'),
  FilesystemBackend = require('i18next-fs-backend'),
  i18nextMiddleware = require('i18next-http-middleware'),
  router = require('express').Router(),
  port = 3000

i18next
  .use(i18nextMiddleware.LanguageDetector)
  .use(FilesystemBackend)
  .init({ preload: ['en', 'de', 'it'], ...otherOptions }, () => {
    i18nextMiddleware.addRoute(
      i18next,
      '/:lng/key-to-translate',
      ['en', 'de', 'it'],
      router,
      'get',
      (req, res) => {
        //endpoint function
      }
    )
    app.use('/', router)
  })
app.use(i18nextMiddleware.handle(i18next))
app.listen(port, () => {
  console.log('Server listening on port', port)
})

custom http server

Define your own functions to handle your custom request or response

middleware.handle(i18next, {
  getPath: (req) => req.path,
  getUrl: (req) => req.url,
  setUrl: (req, url) => req.url = url,
  getQuery: (req) => req.query,
  getParams: (req) => req.params,
  getBody: (req) => req.body,
  setHeader: (res, name, value) => res.setHeader(name, value),
  setContentType: (res, type) => res.contentType(type),
  setStatus: (res, code) => res.status(code),
  send: (res, body) => res.send(body)
})

language detection

Detects user language from current request. Comes with support for:

path
cookie
header
querystring
session

Wiring up:

var i18next = require('i18next')
var middleware = require('i18next-http-middleware')

i18next.use(middleware.LanguageDetector).init(i18nextOptions)

As with all modules you can either pass the constructor function (class) to the i18next.use or a concrete instance.

Detector Options

{
  // order and from where user language should be detected
  order: [/*'path', 'session', */ 'querystring', 'cookie', 'header'],

  // keys or params to lookup language from
  lookupQuerystring: 'lng',
  lookupCookie: 'i18next',
  lookupHeader: 'accept-language',
  lookupSession: 'lng',
  lookupPath: 'lng',
  lookupFromPathIndex: 0,

  // cache user language
  caches: false, // ['cookie']

  // optional expire and domain for set cookie
  cookieExpirationDate: new Date(),
  cookieDomain: 'myDomain',
  cookieSecure: true // if need secure cookie
}

Options can be passed in:

preferred - by setting options.detection in i18next.init:

var i18next = require('i18next')
var middleware = require('i18next-http-middleware')

i18next.use(middleware.LanguageDetector).init({
  detection: options
})

on construction:

var middleware = require('i18next-http-middleware')
var lngDetector = new middleware.LanguageDetector(null, options)

via calling init:

var middleware = require('i18next-http-middleware')

var lngDetector = new middleware.LanguageDetector()
lngDetector.init(options)

Adding own detection functionality

interface

module.exports = {
  name: 'myDetectorsName',

  lookup: function(req, res, options) {
    // options -> are passed in options
    return 'en'
  },

  cacheUserLanguage: function(req, res, lng, options) {
    // options -> are passed in options
    // lng -> current language, will be called after init and on changeLanguage

    // store it
  }
}

adding it

var i18next = require('i18next')
var middleware = require('i18next-http-middleware')

var lngDetector = new middleware.LanguageDetector()
lngDetector.addDetector(myDetector)

i18next.use(lngDetector).init({
  detection: options
})