i18next - multiple express apps

server.js

var i18next = require('i18next');
var middleware = require('i18next-express-middleware');
var Backend = require('i18next-node-fs-backend');
var express = require('express');

i18next
  .use(Backend)
  .init({
    // use correct configuration options...look up docs!
    backend: {
      loadPath: __dirname + '/locales/{{lng}}/{{ns}}.json'
    }
  });

// pseudo virtual hosts
var vhosts = [
  { lng: 'de', port: 3000 },
  { lng: 'en', port: 3001 }
];

vhosts.forEach(function(host) {
  var app = express();

  // set req.lng to defined lng in vhost
  // see for details:
  // https://github.com/i18next/i18next-express-middleware/blob/master/src/index.js#L14
  app.use(function(req, res, next) {
    req.lng = host.lng;
    next();
  });

  // use the middleware to do the magic
  // create a fixed t function for req.lng
  // no clones needed as they just would do the same (sharing all but lng)
  app.use(middleware.handle(i18next));

  // in your request handler
  app.get('/', function(req, res) {
    var lng = req.language;
    var lngs = req.languages;
    console.log('language is: ', lng, lngs);

    res.send(req.t('key1'));
  });


  app.listen(host.port);
});

// go to localhost:3000 ---> de
// go to localhost:3001 ---> en

// unclear to me...why you need an array of express apps to archive this.
// one app with custom language detector function detection lng from domainName
// would be enought to detect lng and translate content appropriate

your issue is related to handlebars being a singleton!

see http://stackoverflow.com/questions/17274142/setting-a-handlebars-helper-to-return-a-specific-value-per-request-in-express

// change the order - first the middleware to get req.t
app.use(middleware.handle(i18next));

// set your lng
// add handlebars helper
app.use(function(req, res, next) {
  req.lng = host.lng; 

  // not sure how you assert in handlebars request save functions...as i always used jade on server
  // which does not suffering from the singleton problem 
  // t helper will be dangerous as race conditions on requests can overwrite it
  // see http://stackoverflow.com/questions/17274142/setting-a-handlebars-helper-to-return-a-specific-value-per-request-in-express
  var handlebars = new ???;
  handlebars.registerHelper('t', function(key, options) {
    var result = req.t(key, options.hash);
    return new handlebars.SafeString(result);
  });

  next();
});

Thanks Jan.

The problem is that req.t is undefined:

app.use(function(req, res, next) {
req.lng = host.lng;

// not sure how you assert in handlebars request save functions...as i always used jade on server
// which does not suffering from the singleton problem
// t helper will be dangerous as race conditions on requests can overwrite it
// see http://stackoverflow.com/questions/17274142/setting-a-handlebars-helper-to-return-a-specific-value-per-request-in-express
var handlebars = new ???;
handlebars.registerHelper('t', function(key, options) {
var result = req.t(key, options.hash); // <========== req.t is undefined.
return new handlebars.SafeString(result);
});

next();
});

We still need a way to retrieve the i18next instance. Going back to the original question. req.t === undefined.

Thanks

req.t === undefined --> gets set by app.use(middleware.handle(i18next));

Hi Jan,

I get this error just by placing this line before as you mentioned:

// change the order - first the middleware to get req.t
app.use(middleware.handle(i18next));

If I do that before :
app.use(function(req, res, next) {
// ...
});

I get:

TypeError: Cannot read property 'indexOf' of undefined
at e.a.value (/Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/i18next/bin/index.js:1:13811)
at t.u.value (/Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/i18next/bin/index.js:2:8308)
at /Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/i18next-express-middleware/lib/index.js:82:40
at Layer.handle as handle_request
at trim_prefix (/Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/express/lib/router/index.js:312:13)
at /Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/express/lib/router/index.js:280:7
at Function.process_params (/Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/express/lib/router/index.js:330:12)
at next (/Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/node_modules/express/lib/router/index.js:271:10)
at /Users/uroblesmellin/projects/bolt20-frontend/bolt-2dot0-frontend/server/middlewares/write-header.js:9:9
at Layer.handle as handle_request

If I do it in the original way (without changing the order of

app.use(middleware.handle(i18next));

I don't get that error.

Thanks,
Ulises