I18N with Aurelia

Getting Started with I18N in your Aurelia App.

Introduction

This documentation explains how to get up and running with Aurelia-I18N in order to provide localization and internationalization features with your app.

Under the hood it uses i18next , which is a generalized open source library with an extensive set of features. By building on top of it not only can you reuse your work across various other platforms and frameworks but you are able to use an extensive eco-system full of various packages.

Installing the Plugin

There are various ways to setup your Aurelia app. It not only boils down to the question whether you use JavaScript or TypeScript but also which module loader and bundler is in use.

Aurelia-I18N is tested and optimized to support both JS and TS, as well as the following loader/bundler scenarios:

  • Aurelia CLI
  • JSPM
  • Webpack

Please continue with the section which suites your setup. In addition to this, you must pick your own backend service. For this guide we're going to leverage the XHR backend plugin , or a variation of this plugin — aurelia-18n-loader — that uses the aurelia loader, which is bundled with the aurelia-i18n plugin. We'll discuss TypeScript specifics in a later section.

Aurelia CLI

In order to install the Plugin with a CLI Project, first install the plugin via npm, from within the root folder of your project:


  npm install aurelia-i18n --save
  

Since Aurelia-I18N is backed by i18next, you should install it and a backend plugin of your choice. You can use the built-in backend that uses aurelia's loader or any of your choice. As an example we're going to leverage the i18next-xhr-backend:


  npm install i18next i18next-xhr-backend --save
  

After that we need to tell our CLI App about the new dependencies. To do so we're going to open the file aurelia_project/aurelia.json and scroll down to the section named dependencies. In there add the following three entries:


  {
    "name": "i18next",
    "path": "../node_modules/i18next/dist/umd",
    "main": "i18next"
  },
  {
    "name": "aurelia-i18n",
    "path": "../node_modules/aurelia-i18n/dist/amd",
    "main": "aurelia-i18n"
  },
  {
    "name": "i18next-xhr-backend",
    "path": "../node_modules/i18next-xhr-backend/dist/umd",
    "main": "i18nextXHRBackend"
  }
  

If you're planning to use the built-in aurelia-i18n-loader there is no need for an additional configuration and you're fine with the first two entries.

JSPM

In your project install the plugin via jspm using the following command:


  jspm install aurelia-i18n
  

And optionally install the backend service using:


  jspm install npm:i18next-xhr-backend
  

You can skip this part if you're planning to use the built-in aurelia-i18n-loader

Webpack

Install the aurelia-i18n plugin in your project using npm and the following command:


  npm install aurelia-i18n --save
  

or if you prefer yarn


  yarn add aurelia-i18n
  

Also optionally install the i18next-xhr-backend plugin:


  npm install i18next-xhr-backend --save
  

or using yarn


  yarn add i18next-xhr-backend
  

You can skip this part if you're planning to use the built-in aurelia-i18n-loader

Optionally, but recommended, add aurelia-i18n to your project's Aurelia bundles list in the webpack.config.babel.js (assuming you used the skeleton-navigation webpack build as your base). This will put the plugin in the Aurelia chunk, not the App chunk.

An example based directly on skeleton-navigation:


  const coreBundles = {
    bootstrap: [/* snip (to keep example short) */],
    aurelia: [
      /* snip (to keep example short) */
      'aurelia-i18n' // add aurelia-i18n to the array
    ]
  }
  

Setting up the Plugin

Now that you have installed and configured your loader, these are the steps to get started with the plugin.

First, use Manual Boostrapping. Open your index.html and locate the element with the attribute aurelia-app. Change it to look like this:


    <body aurelia-app="main">
      ...
    </body>
  

If you're using one of the Aurelia Skeletons as your base this is already done and you can safely skip this step. See here to learn more about manual bootstrapping. .

Second, create a folder named locales in your project's root.

Third, for each locale, create a new folder with it's name (e.g. en, de, ...).

Fourth, in those subfolders create a file named translation.json which contains your language specific translations. Below you can find a sample en-EN translation file. The full potential of i18next is achieved through a specific translation-file schema. Consult the i18next docs to find out more about it.


  {
    "score": "Score: {{score}}",
    "lives": "{{count}} life remaining",
    "lives_plural": "{{count}} lives remaining",
    "lives_indefinite": "a life remaining",
    "lives_plural_indefinite": "some lives remaining",
    "friend": "A friend",
    "friend_male": "A boyfriend",
    "friend_female": "A girlfriend"
  }
  

Fifth, create (if you haven't already) a file main.js in your src folder to configure the plugin. Depending on which backend you've chosen there might be slight differences. The following listings show the configuration for first the built-in aurelia loader, the second using i18next-xhr-backend.

Notice that Aurelia I18N makes use of a non-standard attributes option, which is used to define custom aliases besides the default ones, being t and i18n. Calling TCustomAttribute.configureAliases is currently necessary in order make sure that the aliases are defined before view templates are fully processed.


    import {I18N, Backend, TCustomAttribute} from 'aurelia-i18n';

    export function configure(aurelia) {
      aurelia.use
        .standardConfiguration()
        .developmentLogging()
        .plugin('aurelia-i18n', (instance) => {
          let aliases = ['t', 'i18n'];
          // add aliases for 't' attribute
          TCustomAttribute.configureAliases(aliases);

          // register backend plugin
          instance.i18next.use(Backend.with(aurelia.loader));

          // adapt options to your needs (see http://i18next.com/docs/options/)
          // make sure to return the promise of the setup method, in order to guarantee proper loading
          return instance.setup({
            backend: {                                  // <-- configure backend settings
              loadPath: './locales/{{lng}}/{{ns}}.json', // <-- XHR settings for where to get the files from
            },
            attributes: aliases,
            lng : 'de',
            fallbackLng : 'en',
            debug : false
          });
        });

      aurelia.start().then(a => a.setRoot());
    }
  

    import {I18N, TCustomAttribute} from 'aurelia-i18n';
    import Backend from 'i18next-xhr-backend'; // <-- your previously installed backend plugin

    // if you use TypeScript and target ES5 you might need to import it like this instead
    // import * as Backend from 'i18next-xhr-backend';
    // otherwise add "allowSyntheticDefaultImports": true, to your tsconfig

    export function configure(aurelia) {
      aurelia.use
        .standardConfiguration()
        .developmentLogging()
        .plugin('aurelia-i18n', (instance) => {
          let aliases = ['t', 'i18n'];
          // add aliases for 't' attribute
          TCustomAttribute.configureAliases(aliases);

          // register backend plugin
          instance.i18next.use(Backend);

          // adapt options to your needs (see http://i18next.com/docs/options/)
          // make sure to return the promise of the setup method, in order to guarantee proper loading
          return instance.setup({
            backend: {                                  // <-- configure backend settings
              loadPath: './locales/{{lng}}/{{ns}}.json', // <-- XHR settings for where to get the files from
            },
            attributes: aliases,
            lng : 'de',
            fallbackLng : 'en',
            debug : false
          });
        });

      aurelia.start().then(a => a.setRoot());
    }
  

You may also group your translations by namespaces, spread across multiple files. Say you have the standard translation.json and an additional nav.json for the navigation items, you can configure aurelia-i18n by passing the ns setting in the config object containing the different namespaces as well as the default namespace. When using namespaces, you will need to prepend string references with ns: for those strings that are not in the defaultNS. For example t='nav:profile' would access the profile string in nav.json.


    instance.setup({
      ...
      ns: ['translation','nav'],
      defaultNS: 'translation'
    });
  

Reflect-Metadata Compatibility

If you are using reflect-metadata , there is an outstanding compatibility issue which is resolved by ensuring reflect-metadata is loaded before Aurelia is initialized. If you are using SystemJS, this can be achieved in your index.html as follows:


    <script>
      System.import('reflect-metadata').then( () => {
        System.import('aurelia-bootstrapper');
      });
    </script>
  

TypeScript Support

In order to get proper support for autocompletion and typesafety you should install the necessary type definitions (d.ts) for the plugins dependencies. Here we show how you can do that for i18next and the i18next-xhr-backend, but this should be applicable to every other backend choice.

The way to get hold of those is using using npm or perhaps Yarn as with other packages. In this case the typings are at @types/i18next , along with the instructions. The command is


  npm install --save-dev @types/i18next
  

or if you are using Yarn


  yarn add --dev @types/i18next
  

but in case of yarn there might be a complication as described at https://github.com/yarnpkg/yarn/issues/4226 with a solution proposed to fix complications should they arise.

Alternatively, you can find this file in the plugins repository doc folder: doc/i18next.d.ts

As for the XHR-Backend you'll be using:


  npm install --save-dev @types/i18next-xhr-backend
  

or for yarn


  yarn add --dev @types/i18next-xhr-backend
  

Alternative, you can find this file in the plugins repository doc folder: doc/i18next-xhr-backend.d.ts

Note: if you decide to use the doc/*.d.ts files, you should copy them to another folder, e.g. custom_typings.

If you're running a JSPM setup, in order to properly find the aurelia-i18n.d.ts file, you can alternatively install it via npm:


  npm install --save-dev github:aurelia/i18n
  

The next step is to let the compiler know about your *.d.ts files. Add the following section to your tsconfig.json file.


    ... existing configuration code
    "filesGlob": [
        "./typings/browser.d.ts",
        "./your_custom_typings_folder_path/**/*.d.ts", // if you use both typings files from this repository (`doc/*.d.ts`)
      ],
    ... other existing configuration code
  

or if you are using TypeScript 2.0 or later, you can add them to the types section like %3Cpre%20class%3D%22language-javascript%22%3E%3Ccode%3E%0A%20%20%20%20%3Cspan%20class%3D%22token%20operator%22%3E...%3C/span%3E%20existing%20configuration%20code%0A%20%20%20%20%3Cspan%20class%3D%22token%20string%22%3E%22types%22%3C/span%3E%3Cspan%20class%3D%22token%20punctuation%22%3E%3A%3C/span%3E%20%3Cspan%20class%3D%22token%20punctuation%22%3E%5B%3C/span%3E%20%3Cspan%20class%3D%22token%20string%22%3E%22i18next%22%3C/span%3E%3Cspan%20class%3D%22token%20punctuation%22%3E%2C%3C/span%3E%20%3Cspan%20class%3D%22token%20string%22%3E%22i18next-xhr-backend%22%3C/span%3E%20%3Cspan%20class%3D%22token%20punctuation%22%3E%5D%3C/span%3E%0A%20%20%20%20%20%20%3Cspan%20class%3D%22token%20punctuation%22%3E%5D%3C/span%3E%3Cspan%20class%3D%22token%20punctuation%22%3E%2C%3C/span%3E%0A%20%20%20%20%3Cspan%20class%3D%22token%20operator%22%3E...%3C/span%3E%20other%20existing%20configuration%20code%0A%20%20%3C/code%3E%3C/pre%3E

TypeScript will throw errors like Module xxx not found either for aurelia-i18n or one of the backends. This is due to the fact that TypeScript does not see proper ES6 exported defaults. So you can now either switch to alias imports import * as Backend from 'i18next-xhr-backend' or update your tsconfig with "allowSyntheticDefaultImports": true to maintain the same import style.

Using the Plugin

i18next translations work by setting up an active locale, which you've setup above in the init phase with the property lng.

Setting the active locale

In order to change the active language you'd have to call the function setLocale(localeName) via code.


    import {I18N} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [I18N];
      constructor(i18n) {
        this.i18n = i18n;
        this.i18n
            .setLocale('de-DE')
            .then( () => {
          // locale is loaded
        });
      }
      ...
    }
  

Getting the active locale

To get the active locale you'd go with getLocale():


    import {I18N} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [I18N];
      constructor(i18n) {
        this.i18n = i18n;
        console.log(this.i18n.getLocale());
      }
      ...
    }
  

Translating via code

Translating stuff via code works by using the method tr. You pass in the key as its first parameter, followed by the optional second parameter options to specify in detail how the translations should be performed. Please consult the i18next docs for a detailed list of those:


    import {I18N} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [I18N];
      constructor(i18n) {
        this.i18n = i18n;
        console.log(this.i18n.tr('mykey'));
      }
      ...
    }
  

Translating via html attributes

Translation in html can be done alternatively using attributes. By default the plugin is configured to use the t and i18n attributes. This can be configured during the plugin registration using the TCustomAttribute.configureAliases function and also the attributes property plugin instance.setup function parameter.


    ...
    .plugin("aurelia-i18n", (instance) => {
      ...
      let aliases = ['t','i18n'];
      TCustomAttribute.configureAliases(aliases);
      ...
      instance.setup({
      ...
        attributes : aliases,
      ...
      });
      ...
    });
    ...
  

Passing the option skipTranslationOnMissingKey during plugin initialization, will keep your original contents in place and instead add a warning in the console about trying to update an element without a matching key.

Any element in your views that has one of those attributes, will be translated when the locale is changed.


    <span t="title">Title</span>
  

The plugin will use the title as the key when translating that element. Other attributes, specified in the attributes option, may be used as well.


    <span i18n="home.title">Title</span>
  

Notice in the above example that the key was set to home.title. This will make the plugin look for a translation with nested objects in your translation json, ie:


    {
      "home": {
        "title": "Title",
      }
    }
  

Use updateTranslation() to update all translations within the children of the element that is passed to it. The following example shows how a view model can be configured to update it's contents when the view is attached and every time a locale is changed.


    import {I18N} from 'aurelia-i18n';
    import {EventAggregator} from 'aurelia-event-aggregator';

    export class MyDemoVM {
      static inject = [I18N,Element,EventAggregator];
      constructor(i18n,element,ea) {
        this.i18n = i18n;
        this.element = element;

        ea.subscribe('i18n:locale:changed', payload => {
          this.i18n.updateTranslations(this.element);
        });
      }

      attached(){
        this.i18n.updateTranslations(this.element);
      }
    }
  

Alternatively you may extend your VM with the provided Base-I18N-VM, which will set that up for you automatically.


    import {BaseI18N} from 'aurelia-i18n';

    export class MyDemoVM extends BaseI18N {

    }
  

Just remember in case you define your own constructor, to call this.super and pass it the instances of its dependencies as described in the previous example. Same applies to attached, although nothing needs to be passed in here

Specifying attributes

By default the plugin will set the textContent property of an element.


  //translation
  {
    "title": "Title <b>bold</b>"
  }
  
  //markup
  <span t="title">Title</span>
  

So in above example the html tags will be escaped and the output will be &lt;b&gt;bold&lt;/b&gt;. To allow html-markup to be used, the [html] attribute needs to be added before the translation key.


  <span t="[html]title">Title</span>
  

This will set the innerHTML of the element instead of the textContent property, so html-markup won't be escaped. There are 4 special attributes including the shown [html]:

  • [text]: Sets the textContent property (default)
  • [html]: Sets the innerHTML property
  • [append]: appends the translation to the current content already present in the element (allows html).
  • [prepend]: prepends the translation to the current content already present in the element (allows html).

If the element is a custom element and the value relates to a bindable property of that, then the properties value itself will be updated.


  // Custom Element ViewModel
  export class Foo {
    @bindable() mybindable = "abc";
  }
  
  // Custom Element View
  <template>
    <span>${'mybindable'}</span>
  </template>
  
  // Rendering the Custom Element and passing validations to custom bindable properties
  <foo t="[mybindable]bar"></foo>
  
  // Result
  <foo>
    <span>[TRANSLATED VALUE OF BAR KEY]</span>
  </foo>
  

Any other values will be used as actual attributes on the element itself. The following example will not change the content of the element, but will set its alt attribute to the translated value of title when the locale changes.


  <span t="[alt]title">Title</span>
  

Specifying multiple attributes

Multiple attributes can be specified by separating them with a semicolon.


  <span t="[html]title;[class]title-class">Title</span>
  

When the locale changes it will set the innerHTML to the translated value of title due to the [html] attribute and the class property to the translated value of title-class.

Using nested and combined translations

In order to combine two or more translations, just include them with the $t(yourkey) markup


  <span t="$t(title) $t(subtitle)">Title subtitle</span>
  

Nested keys may also be referenced and will be properly translated:


    {
      "translation": {
        "title": "Title",
        "nested_referencing": 'The $t(title) is the header',
        ...
      }
    }
  

  <span t="nested_referencing">Nested text</span>
  

Translating images

Images can be translated as well, for when a different image needs to be displayed in another language.


  <img t="home.image">
  

The plugin will automatically change the src attribute of the image when the locale changes.

You may specify a default value for images as well. In order to do so just define an attribute called data-src with the default value.


  <img data-src="path/to/image.jpg" t="home.image">
  

This will be picked up by the CLI when translations are extracted from the source files. (see the section on CLI Integration)

Passing parameters to the attribute

In order to use parameters for replaceable parts in your translation key, you can provide an additional t-params attribute and bind it to the object containing the replacement values. Also note that for whatever attribute you registered, the corresponding *-params attribute will get registered as well automatically.


  // Translation file
  {
    "paramstest": "Some text with <strong>{{content}}</strong>"
  }
  

     View 
    <span t="[html]paramstest" t-params.bind="params"></span>
  

  // ViewModel
  class MyVM {
    params = { content: 'ABC' }
  
    [...]
  }
  

The object passed to t-params is a complex object explained in the next section. To use it via code, see Complex objects for variables via code.

Translating with the TValueConverter

In order to do translations in a more declarative way from within your HTML markup you can use a custom ValueConverter named t. It takes exactly the same options as the code translation method tr but of course provides the key automatically.

You will find below a few examples of the available i18next features


    <template>
      <section>
        <div class="row">
          <div class="col-md-3">
            <h3>ValueConverter Examples</h3>
            <ul class="list-group">
              <li class="list-group-item">
                Translation with Variables: <br />
                ${ 'score' | t: {'score': userScore}}
              </li>

              <li class="list-group-item">
                Translation singular: <br />
                ${ 'lives' | t: { 'count': 1 } }
              </li>

              <li class="list-group-item">
                Translation plural: <br />
                ${ 'lives' | t: { 'count': 2 } }
              </li>

              <li class="list-group-item">
                Translation singular indefinite: <br />
                ${ 'lives' | t: { 'count': 1, indefinite_article: true  } }
              </li>

              <li class="list-group-item">
                Translation plural indefinite: <br />
                ${ 'lives' | t: { 'count': 2, indefinite_article: true } }
              </li>

              <li class="list-group-item">
                Translation without/with context: <br />
                ${ 'friend' | t } <br />
                ${ 'friend' | t: { context: 'male' } } <br />
                ${ 'friend' | t: { context: 'female' } }
              </li>
            </ul>
          </div>
        </div>
      </section>
    </template>
  

Translating with the TBindingBehavior

The TValueConverter is pretty useful if you prefer a declarative way to enhance DOM elements with i18n support. But it has a lack when it comes to automatically updating itself when changes happen outside, like locale switches. This is what the TBindingBehavior can do. Essentially you do the same thing like with the TValueConverter but use the & sign instead of | to indicate usage of the binding behavior.


  <li class="list-group-item">
    Translation with Variables: <br />
    ${ 'score' & t: {'score': userScore}}
  </li>
  

Now aurelia-i18n will automatically emit signals when internal changes happen and you can do so as well by emiting a aurelia-translation-signal. The following example depicts how this is done internally when the current locale changes. First you need to get hold of the BindingSignaler exported by the aurelia-templating-resources module and inject it either in your constructor or via the static $inject property. Next when you want to trigger the signal just use the signalers signal method and pass it the predefined string.


    import {BindingSignaler} from 'aurelia-templating-resources';
    // inject signaler to constructor ...
    ...

    setLocale(locale) {
      return new Promise( resolve => {
        let oldLocale = this.getLocale();
        this.i18next.setLng(locale, tr => {
          this.ea.publish('i18n:locale:changed', { oldValue: oldLocale, newValue: locale });
          this.signaler.signal('aurelia-translation-signal');
          resolve(tr);
        });
      });
    }
  

If you want to only update your relative time binding behaviors, you may use the signal aurelia-relativetime-signal which will only trigger those and safe unnecessary update roundtrips

Complex objects for variables via code

In some cases it might be useful to define variables via complex objects. Let's take a look at below example. It shows a validation message to hint the user that a given field should be in range of min and max. Now we could easily pass min and max as separate variables but on the other hand that involves more work you'd have to do manually if the source is a object.


    var resources = {
      en: {
        translation: {
          "complex": '{{field}} should be between {{threshold.min}} and {{threshold.max}}'
        }
      }
    };
  

So in order to avoid that you may simply pass in the object as a whole and the library will pickup all the necessary information and create the proper options object. You can also mix and match it with simple variables.


    var options = {
      'threshold': {
        'min': 1,
        'max': 10
      },
      'field': 'Age'
    };

    i18n.tr('complex', options);
    // --> Age should be between 1 and 10
  

Formatting numbers via code

For displaying numbers in different formats, this plugin makes use of the Internationalization API NumberFormat . It leverages the same locales used for the translation methods mentioned in the install process of the plugin.

The API provides access to the Intl NumberFormat with the method NumberFormat. This function takes the an options object representing the formatting options as the first and the locale as the second parameter.

Below is an example how to access the NumberFormat via code:


    import {I18N} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [I18N];
      constructor(i18n) {
        this.i18n = i18n;

        // create a NumberFormat with German locale
        var nf = this.i18n.nf(undefined, 'de');
        var result = nf.format(123456.123);

        console.log(result);
        // output => 123.456,123


        // create a NumberFormat with currency options
        var nf = this.i18n.NumberFormat({ style: 'currency', currency: 'EUR' }, 'de');

        var result = nf.format(123456.123);

        console.log(result);
        // output => 123.456,123 €
      }
      ...
    }
  

Formatting numbers with NfValueConverter

A more declarative way is to use the nf ValueConverter from within your HTML markup. It essentially works the same way as the code version. Take a look at the following example:


    <div class="col-md-3">
      <h3>ValueConverter Number Examples</h3>
      <ul class="list-group">
        <li class="list-group-item">
          Numberformat with default locale/format:
          ${ 1234567.890 | nf : undefined : selectedLocale}
        </li>
        <li class="list-group-item">
          Numberformat with different locale default format:
          ${ 1234567.890 | nf : undefined : 'de'}
        </li>
        <li class="list-group-item">
          Numberformat with different locale/format:
          ${ 1234567.890 | nf : { style: 'currency', currency: 'EUR' } : 'de'}
        </li>
      </ul>
    </div>
  

If you provide the active locale as a bound VM property, the ValueConverter will be re-evaluated as soon as the property value changes, resulting in automatic re-formatting of your number.

Formatting dates via code

The Intl. API provides means to format DateTimes as well. Use the method df to access that feature with the same arguments used for NumberFormat Below you'll find an example how to use those via code:


    import {I18N} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [I18N];
      constructor(i18n) {
        this.i18n = i18n;

        // create a DateTimeFormat with German locale
        var df = this.i18n.df(undefined, 'de');
        var result = df.format(new Date(2000, 0, 1, 0,0,1))

        console.log(result);
        // output => 1.1.2000


        // create a DateTime with time and 2-digit display
        var options = {
          year: 'numeric', month: '2-digit', day: '2-digit',
          hour: '2-digit', minute: '2-digit', second: '2-digit',
          hour12: false
        };
        var df = this.i18n.df(options, 'de');

        var result = df.format(new Date(2000, 0, 1, 0,0,1));

        console.log(result);
        // output => 01.01.2000 00:00:01
      }
      ...
    }
  

Remember that if you pass in undefined for the options parameter you'll get the default formatting options

Formatting dates with DfValueConverter

A more declarative way is to use the df ValueConverter from within your HTML markup. It essentially works the same way as the code version. Take a look at the following example, which defines a VM property myDate:


    <div class="col-md-3">
      <h3>ValueConverter Date Examples</h3>
      <ul class="list-group">
        <li class="list-group-item">
          DateFormat with default locale/format:
          ${ myDate | df : undefined : selectedLocale}
        </li>
        <li class="list-group-item">
          DateFormat with different locale default format:
          ${ myDate | df : undefined : 'de'}
        </li>
        <li class="list-group-item">
          DateFormat with different locale/format:
          ${ myDate | df : { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' } : 'de'}
        </li>
      </ul>
    </div>
  

Rendering relative time

In order to create a representation of relative time like x days ago or in x days you can leverage the Service relativeTime. This exposes a method getRelativeTime which accepts a valid JS date. To use it via code get hold of the service via injection and call the method as needed:


    import {RelativeTime} from 'aurelia-i18n';

    export class MyDemoVM {
      static inject = [RelativeTime];
      constructor(relativeTime) {
        this.rt = relativeTime;

        var myDate = new Date();
        myDate.setHours(myDate.getHours() - 2);

        var result = relativeTime.getRelativeTime(myDate);

        console.log(result);
        // output => 2 hours ago
      }
      ...
    }
  

This is also tied in to the currentLocale of the library so changing that one will also translate relative time messages. Take a look at the file src/defaultTranslations/relative.time.js for available translations. If you're missing yours, I welcome you to provide a PR so everybody can benefit from it.

A more declarative approach is to use the RtValueConverter directly in your HTML markup. It doesn't take any additional parameters, so just drop it in and you're good to go:


    <div class="col-md-3">
      <h3>ValueConverter Relative Time Examples</h3>
      <ul class="list-group">
        <li class="list-group-item">
          2 hours ago:
          ${ myDate | rt }
        </li>
      </ul>
    </div>
  

Bundle Translation Files

When bundling is used, the built-in backend will read the translations from the bundle with the aurelia loader. Make sure that the translation.json files are packed in the bundle using the text module, by changing the aurelia.json and adding .json as an extension for the text plugin:


  "loader": {
  	"type": "require",
  	"configTarget": "vendor-bundle.js",
  	"includeBundleMetadataInConfig": "auto",
  	"plugins": [
  		{
  			"name": "text",
  			"extensions": [
  				".html",
  				".css",
  				".json"
  			],
  			"stub": true
  		}
  	]
  },
  

Using JSPM

If you're using JSPM as your module loader, the bundle configuration might look like.


  "bundles": {
    "dist/app-build": {
     "includes": [
       "[*.js]",
       "*.html!text",
       "*.css!text",
       "*.json!text"
     ],
  

Using Aurelia CLI

Same would apply to the Aurelia CLI. In order to tell it to process the locales you can create a new task process-locales.js, located in the aurelia_project/tasks folder with the contents:


    import gulp from 'gulp';
    import changedInPlace from 'gulp-changed-in-place';
    import project from '../aurelia.json';
    import {build} from 'aurelia-cli';

    export default function processLocales() {
      return gulp.src(project.localesProcessor.source)
        .pipe(changedInPlace({firstPass: true}))
        .pipe(build.bundle());
    }
  

With that in place, edit your aurelia_project/aurelia.json file and add the task right after the markupProcessor configuration, where the source property should reflect your previously setup locales folder:


  ...
  "localesProcessor": {
    "id": "none",
    "displayName": "None",
    "fileExtension": ".json",
    "source": "src/locales/**/*.json"
  },
  ...
  

Also, edit your aurelia_project/tasks/run.js (or .ts if you're using Typescript) file and add a new gulp.watch task to the watch function:


    let watch = function() {
      gulp.watch(project.transpiler.source, refresh).on('change', onChange);
      gulp.watch(project.markupProcessor.source, refresh).on('change', onChange);
      gulp.watch(project.cssProcessor.source, refresh).on('change', onChange);
      gulp.watch(project.localesProcessor.source, refresh).on('change', onChange); //<-- add this line
    };
  

By doing this, if you're running your project with the --watch flag, your bundles will be rebuilt whenever your change something in your translation files. In the same way that happens with your .html, .js and .css files.

Last but not least search for the build/bundles/source section for the app-bundle and update the configuration to include json files.


  ...
  "bundles": [
    {
      "name": "app-bundle.js",
      "source": [
        "[**/*.js]",
        "**/*.{css,html,json}"
      ]
    }
    ...
  ]
  

and inlcude the json extension in the loader plugin part build/loader/plugins/extensions


  ...
  "plugins": [
    {
      "name": "text",
      "extensions": [
        ".html",
        ".css",
        ".json"
      ],
      "stub": true
    }
  ]
  ...
  

Internationalization API Polyfill

The plugin leverages the JavaScript Internationalization API to perform certain tasks. Since not all browsers do fully support it ( compatibility table ) the aurelia-i18n conditionally loads the Polyfill if needed.

In case of bundling your app you should thus keep in mind that it will not be automatically included into the bundle. That means you have to manually adjust the bundle config to include the polyfill as well, if you intend to have your application run on browsers without full support. related GitHub issue

Bundling the Intl Polyfill with Aurelia CLI

Aurelia-I18N uses a polyfill to provide Intl.API support for browsers currently not implementing the feature. Amongst those are Safari for Mac and iOS. The Polyfill will be lazy loaded in dev mode as needed but won't be included automatically as part of the bundle. The reason is the decent file size of ~50k in minified mode, as such you as the developer have to opt-in and bundle the Polyfill manually.

To do so first install the Polyfill as part of your project using npm:


  npm install intl --save
  

After that open up the aurelia_project/aurelia.json file and add the following dependency:


  {
    "name": "intl",
    "path": "../node_modules/intl/dist",
    "main": "Intl.min"  // or Intl.complete
  },
  

Instead of referencing the min file you could also reference Intl.complete to include the Unicode CLDR locale data. For more info about that consult the official Polyfill docs .

Use Internationalization API Polyfill with Webpack

In order to use the Polyfill with Webpack, you will have to adapt your bootstrap function.


    bootstrap(aurelia => {
      if (!global.Intl) {
        console.log('Intl not present')
        require.ensure([
          'intl',
          'intl/locale-data/jsonp/en.js'
        ], function (require) {
          require('intl');
          require('intl/locale-data/jsonp/en.js');
          boot(aurelia);
        });
      } else {
        boot(aurelia);
      }
    });

    function boot(aurelia) {
      aurelia.use
        .standardConfiguration()
        .developmentLogging()
        .plugin('aurelia-i18n', (instance) => {
            // code to setup aurelia-i18n
        });

      aurelia.start().then(() => aurelia.setRoot('app', document.body));
    }
  

When using WebPack, one needs to add PLATFORM.modulename to enable aurelia-webpack-plugin to properly recognize the plugins. With that change, the example code looks like so:


    bootstrap(aurelia => {
      if (!global.Intl) {
        console.log('Intl not present')
        require.ensure([
          'intl',
          'intl/locale-data/jsonp/en.js'
        ], function (require) {
          require('intl');
          require('intl/locale-data/jsonp/en.js');
          boot(aurelia);
        });
      } else {
        boot(aurelia);
      }
    });

    function boot(aurelia) {
      aurelia.use
        .standardConfiguration()
        .developmentLogging()
        .plugin(PLATFORM.modulename('aurelia-i18n'), (instance) => {
            // code to setup aurelia-i18n
        });

      aurelia.start().then(() => aurelia.setRoot('app', document.body));
    }
  

Or using TypeScript


 aurelia.use
        .standardConfiguration()
        .developmentLogging()
        .plugin(PLATFORM.moduleName('aurelia-i18n'), (instance: I18N) =>
            // code to setup aurelia-i18n
        });

      await aurelia.start();
      await aurelia.setRoot('app', document.body);
    }
      

More information in the README of the Intl.js polyfill .

On top of that if you need the Intl polyfill included you have to manualy require and bundle it. To do so add the following import statement at the begin of your main.js/ts file:


    //main.js
    import 'intl';
  

For additional information about Intl.js and Webpack please take a look at this official repos information