Fetch i18next translations with the fetch API
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This is a simple i18next backend to be used in the browser. It will load resources from a backend server using the fetch API.

Getting started

This backend is most useful when XMLHttpRequest is not available, such as with Service Worker contexts. It is also useful when support for older browsers is not a concern, and newer APIs are a priority. Source can be loaded via npm.

# npm package
$ npm install --save i18next-fetch-backend

Wiring up:

import i18next from 'i18next';
import Fetch from 'i18next-fetch-backend';

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

Backend Options

  // path where resources get loaded from, or a function
  // returning a path:
  // function(lngs, namespaces) { return customPath; }
  // the returned path will interpolate lng, ns if provided like giving a static path
  loadPath: '/locales/{{lng}}/{{ns}}.json',

  // parse data after it has been fetched
  // in example use https://www.npmjs.com/package/json5
  // here it removes the letter a from the json (bad idea)
  parse: function(data) { return data.replace(/a/g, ''); },

  // path to post missing resources
  addPath: 'locales/add/{{lng}}/{{ns}}',

  // define how to stringify the data when adding missing resources
  stringify: JSON.stringify,

  // your backend server supports multiloading
  // /locales/resources.json?lng=de+en&ns=ns1+ns2
  allowMultiLoading: false, // set loadPath: '/locales/resources.json?lng={{lng}}&ns={{ns}}' to adapt to multiLoading

  multiSeparator: '+',

  // init option for fetch, for example
  requestOptions: {
    mode: 'cors',
    credentials: 'same-origin',
    cache: 'default',

  // define a custom fetch function
  fetch: function (url, options, callback) {},

Options can be passed in:

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

import i18next from 'i18next';
import Fetch from 'i18next-fetch-backend';

    backend: options

on construction:

  import Fetch from 'i18next-fetch-backend';
  const fetch = new Fetch(null, options);

via calling init:

  import Fetch from 'i18next-fetch-backend';
  const fetch = new Fetch();

Service Worker example

import i18next from 'i18next';
import Fetch from 'i18next-fetch-backend';

let t = null;

self.addEventListener('activate', (event) => {
  event.waitUntil(new Promise((resolve, reject) => {
        fallbackLng: ['ja', 'en', 'zh'],
        preload: ['ja', 'en', 'zh'],
        ns: 'translation',
        defaultNS: 'translation',
        keySeparator: false, // Allow usage of dots in keys
        nsSeparator: false,
        backend: {
          loadPath: '/locales/{{lng}}/{{ns}}.json',
      }, (err, _t) => {
        if (err) {

        t = _t;