How to reuse i18next instance in an express app - express

Question

I have an express backend that I want to internationalise. I want to:
init my i18next instance at one place
reuse that instance on multiple places in code
I want to use them also in model code, not only in routes
This might sound like a primitive question, but even after reading through the i18next docs, I still don't know how I should reuse the initialised i18next instance. If I use i18next-express-middleware, I can use the t() method in routes. Fine, but what do I do if I want to use it in the models or some other file, let's say in model?
I dislike the idea of passing it down to every model method via a parameter. I cannot simply do import i18next from 'i18next' in each file, because it would return a new instance. I can't make js-file where I would init the instance in an async function and then return it, because I can't call an async function via await in the app.js (root file of my express app). Am I trying to force it on a use case for which it wasn't built?
Thank you for any tips.

Answer 1

In app.js:
const express = require('express');
const i18next = require('i18next');
const i18nextMiddleware = require('i18next-express-middleware');
const app = express();
First configure i18next
i18next
.use(i18nextMiddleware.LanguageDetector)
.init({
preload: ['de', 'en'],
fallbackLng: 'en',
resources: {
en: {
translation: {
key: 'hello world'
}
}, // ...
},
detection: {
// 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: `${config.Host.hostname.replace(/^https?:\/\//, '')}`,
cookieSecure: true // if need secure cookie
}
});
Then register the middleware:
app.use(
i18nextMiddleware.handle(i18next, {
// options
})
);
And add a custom middleware for setting i18next instance:
app.use((req, res, next) => {
i18next.changeLanguage(req.language);
});
Gathered from documentation at
expressjs.com/en/guide/using-middleware.html
github.com/i18next/i18next
github.com/i18next/i18next-express-middleware