The core of gengo.js that manages i18n and l10n.

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<script type="module">
  import gengojsCore from '';



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The core of gengo.js that manages i18n and l10n.


See documentation.



Another release!? Yup and it's going fast. 1.0.0-alpha.2 has already been released but expect more alphas to be released within this month. Also, I have released sails-hook-gengojs on npm which will allow you to use gengo.js in your Sails app as if it was built into Sails in the first place. In future releases expect gengo.js to move from alpha -> beta -> rc (release candidate). I will also be working on so expect that to happen soon as well! Well, happy coding!


Greetings! As promised, I have added documentation to the core and to the plugins. It should be self explanatory but if there is something that needs clarification then feel free to create an issue about it. As far as gengo.js is concernced, expect 1.0.0-alpha.2 to be released within this week or next (hopefully soon). I'll also be creating an example app with Sails so that it will show how gengo.js works. I do plan to create a sails hook that will replace the default i18n of sails so be watching! ;) In the mean time, please checkout the documentations of the plugins. Anyways, happy coding!


Hey! First of all, apologies for any delays in gengo.js. I've been working on another project called Mr Doc. It's a tool that generates beautiful docs and I've improved it because I really needed a better way to document my source. So I hope to go through everything as I document them well. Some changes did occur as I was working on Mr. Doc. I've decided to move all gengo.js related projects from my personal Github account to a dedicated account. There, you will find everthing you need to work on gengo and contribute. Finally, I did generate the docs for the core so see Documentation. Well, that's all for now! Happy coding!

As of 8/29/15, I've decided to go through the core and the plugins and refine them so that it will be easier to create the docs and hopefully easier to understand how to create plugins.

Some from the docs below may still work as far as exporting plugins but the idea of internal API still needs some refinement.


gengojs-core is the actual core of gengo.js. It serves to be a server agnostic middle-ware supporting the popular servers such as Express, Koa, Hapi, and even more with ease. It is also modular-tastic, and easy to debug with less than 40 lines of source code according to sloc.

To get started, there are three things to know about how the core works:

  • Initialize
  • Ship
  • Parse

Initialize is the starting point of the core. It handles the initialization of the plugin's stack, options, and also the back-end. The reason the back-end is initialized first is because of the possible use of asynchronous programming needs. Note that if you are to create a plugin for the back-end, you will need to load every locale into memory so that the parser can readily use the data.

Ship is a function that applies the API to requests and also to the view. It begins by getting the locale from the client, letting the router know about the current URL path, applying the locale to the localization plugin, and finally assigning the API such as __ or __l (can be changed) to the objects that are provided by the request and response..

Parse is the final step in the core. It is called only when the API such as __('Hello') are used. In this step, the parser plugin must return the i18ned string.

So... you may be wondering why is the core a separate module from the rest? The reason is because having the core on its own allows you, developers, to create awesome plugins. I personally feel as if i18n modules are a bit limited in what it can do and myself as well.

Anyways, one thing to note is that this module should not be used on its own. The actual i18n library is gengo.js. If you want to extend the core to support server x, then here is where you want to do that but if you want to create the wrapper for server x, then gengo.js is where you would do that.

Getting Started

How gengo.js works is similar to how Hapi works in terms of creating plugins and how Grunt works in terms of options.

To create plugins, the one thing to keep in mind is core's this context. When a plugin is initialized, the core calls the plugin as it binds its context to that plugin (see Creating Plugins). Another thing to keep in mind is dependency. Dependencies are really internal API. For example, the parser plugin needs to know about the data. Therefore it is dependent on the back-end plugin and is expecting the back-end to supply an internal API to retrieve the locale/data. To see how dependencies work, checkout the default plugins. Each plugin show the dependencies and the exposed internal api and also have their own documentation.

Creating Plugins

Creating plugins is quite similar, if not, the same as creating plugins for Hapi. As mentioned above, the core is really all about context. The following shows you the recommended way to create your plugins:

For this example we will create a dummy header plugin:


function MyHeaderClass (options){

   this.getLocale = function(){
    // ...


class MyHeaderClass {
  constructor (options){
    // ...
    // ...

Exporting Plugins

Now we will export our dummy header plugin. Our plugin must specify a type which we know it's a header but here are the available types:

  • parser
  • header
  • api
  • localize
  • backend
  • router

In this example, I will use Lodash to merge the type of plugin with the package.

Our plugin must also have defaults provided.

module.exports = function ship() {
 var pkg = require('./package');
  return {
    main: function ship(){
      // Pass options and expose internal API
      this.header = new MyHeaderClass(this.options.header);
    package: _.merge({
      type: 'header'
    }, require('../package')),,
    // Provide option defaults
    defaults: require('./defaults.json')


  • You may have noticed that defaults are provided in the example. Defaults are required (See Options). If you do not have any defaults, then you can just pass {}, and the core will not complain.

  • Keep in mind that you are limited to one plugin per type. This was done to prevent problems that may arise when dealing with the core's context.

Exporting Multiple Plugins

Now you may be wondering, Can I release a set of plugins? The answer is YES!. I call these sets, packs or gengo-pack. To create a pack, simply export the individual ships like the following:

module.exports = function(){
  return {
    parser: /*parser ship*/,
    router: /*router ship*/,
    backend: /*backend ship*/,
    api: /*api ship*/,
    header: /*header ship*/,
    localize: /*localize ship*/

Testing your plugins

To test your plugins, simply install the core and also the default plugins needed for your plugin. The simplest way to require all the default plugins is by installing gengojs-default-pack which contains all the default plugins. Since the pack is an object, you can simply use it like so:

var pack = require('gengojs-default-pack');

// Use only what you need
var header = pack.header;
var backend = pack.backend;
// or you can just replace the plugin:
pack.backend = myBackendPlugin;

// Then use the core for tests

var core = require('gengojs-core');

var gengo = core({}, pack);

// Test for your plugins existence:

// ...


The core doesn't have the best option system but the official way to access options per plugin is by the context as in the example:

function ship(){
  // To access the options,
  // simply use: this.options[type]:

In general, you can access any other plugin's options through the same syntax as in the example, but make sure to provide the defaults when you create your plugins. The core will apply them to the options as soon as it loads the plugin.


Feel free to contribute. To contribute, see the requirements. If you have any suggestions, create issues at the core's GitHub Issues. Also, all ES6 modules are located under lib/.


The core uses gengojs-debug, an extension of debug, to output debugging statements. To debug, simply set the type of debug in the shell:


$ DEBUG=gengo.core:*


$ SET DEBUG=gengo.core:*

The levels used in the core are:

  • debug
  • error
  • info


# Build modules with gulp for development


# Build modules with gulp for production
gulp test


See changelog.