I18n-behavior NPM

i18n-behavior

Instant and Modular I18N engine for lit-html and Polymer

html`` tagged template literal API is provided by i18n-element

Compatible Versions

Polymer library (@polymer/polymer NPM package) is configured as a peer dependency since 4.0.0
Polymer elements using I18nBehavior must depend on @polymer/polymer NPM package themselves

i18n-behavior	i18n-element	Polymer	lit-html
5.x	5.x	3.x (optional)	2.x
4.x	4.x	3.x (optional)	1.x
3.x	3.x	3.x (mandatory)	1.x
2.x	2.x	1.x-2.x	-
1.x	-	1.x	-

Changelog

Browser Compatibility

TODO: To be updated

Browser	Chrome	Firefox	Edge 13+	IE 11	Safari 10+	Chrome Android	Mobile Safari	Opera
Supported	✔	✔	✔	✔	✔	✔	✔	✔

Polyfilled by @webcomponents/webcomponentsjs/webcomponents-{bundle|loader}.js

Conceptual Workflow

demo/gulpfile.js provides support for extracting UI strings from html tagged template literals in JavaScript sources as well as Polymer HTML templates in HTML Imports

Install

    npm install i18n-behavior

Import for Polymer elements

    import { I18nBehavior } from 'i18n-behavior/i18n-behavior.js'

Quick Tour

I18N-ready pwa-starter-kit

    npm install -g polymer-cli
    git clone https://github.com/t2ym/pwa-starter-kit
    cd pwa-starter-kit
    npm ci
    # Add Locales
    gulp locales --targets="de es fr ja zh-Hans"
    # I18N Process
    gulp
    # Translate XLIFF ./xliff/bundle.*.xlf
    # Merge Translation
    gulp
    # Dev build on http://localhost:8080
    polymer serve
    # Static build
    polymer build
    # Static build on http://localhost:8080
    cd build/{esm-unbundled|esm-bundled|es6-bundled|es5-bundled}
    python -m SimpleHTTPServer -p 8080

Usage in Polymer legacy syntax

API Docs
Demo
ES6 class syntax support is provided by i18n-element

Run-time Automatic I18N

Apply BehaviorsStore.I18nBehavior or imported I18nBehavior

Source Code

    // Legacy Polymer syntax
    Polymer({
      importMeta: import.meta,
      is: 'custom-element',
      _template: html`
        <span id="label">UI text label</span> <!-- no need to touch UI text strings -->
      `,
      behaviors: [
        I18nBehavior // Add this line for I18N
      ]
    });

I18N-ready preprocessed DOM at element registration

Hard-coded UI text strings are automatically extracted and replaced with annotations bound to text object.

lang attribute specifies the current locale. By default, <html lang> attribute is observed and mirrored to those for I18N-ready element instances.

    <html lang="en"><!-- html lang attribute is observed and mirrored -->
      ...
      <custom-element lang="en">
        <span id="label">{{text.label}}</span><!-- UI texts are bound to text object -->
      </custom-element>
      ...
    </html>

If the containing element of the target text has id attribute, the string id is named with the id value. If not, the string id is automatically generated. It is recommended to put meaningful id to each string for robustness. When attaching id attribute is too much for the containing element, text-id attribute can be used instead.

    <span text-id="label">{{text.label}}</span>

`text` dynamic property

this.text dynamic object property represents an object with UI text strings for the current locale.

    this.text = {
      "label": "UI Text Label"
    }

this.text dynamic object is SHARED among all the instances of the same custom element.

`model` dynamic property

this.model is deepcopied from this.text.model per instance to store I18N target attribute values. UI text strings in I18N target attributes are automatically extracted and replaced with annotations according to the shared repository (i18n-attr-repo) of I18N target attributes per elements (like placeholder attribute of input element).

On lang-updated event, this.text.model is updated but this.model is NOT automatically updated and needs explicit update like this.

    listeners: {
      'lang-updated': '_langUpdated'
    },

    _langUpdated: function (event) {
      if (Polymer.dom(event).rootTarget === this) {
        this.model = deepcopy(this.text.model);
      }
    }

`<json-data>` for manual text definitions

Optionally, any JSON data can be manually added to I18N target strings via <json-data> element. This option is effective for manual extraction of hard-coded UI text strings in JavaScript literals.

  <dom-module id="my-element">
    <template>
      ... <!-- ordinary template for rendering -->
      <template><!-- containing template element to avoid rendering -->
        <json-data id="items">[
          "Responsive Web App boilerplate",
          "Iron Elements and Paper Elements",
          "End-to-end Build Tooling (including Vulcanize)",
          "Unit testing with Web Component Tester",
          "Routing with Page.js",
          "Offline support with the Platinum Service Worker Elements"
        ]</json-data>
        <json-data id="sender">{ "name": "Sam", "gender": "male" }</json-data>
      </template>
    </template>
    <script>
    ...
    this.text.items[0] === 'Responsive Web App boilerplate'
    this.text.sender.name === 'Sam'
    ...
    </script>
  </dom-module>

Localized text strings fetched from JSON

While default text strings are extracted from the hard-coded strings in HTML template, localized text strings are asynchronously fetched from JSON files under locales directory at the server.

    /bundle.json
    /locales/bundle.ja.json
            /bundle.fr.json
            /bundle.zh-Hans.json
    
    /elements/my-list/my-list.json
                     /locales/my-list.ja.json
                             /my-list.zh-Hans.json
    
             /google-chart-demo/google-chart-demo.json
                               /locales/google-chart-demo.ja.json
                                       /google-chart-demo.fr.json

Build-time Automatic I18N

gulp-i18n-preprocess filter performs build-time automatic I18N and embeds UI texts as JSON.

I18N-ready Source Code preprocessed by gulp-i18n-preprocess:

    <dom-module id="custom-element">
      <template localizable-text="embedded">
        <span id="label">{{text.label}}</span>
        <template id="localizable-text">
          <json-data>{
            "label": "UI Text Label"
          }</json-data>
        </template>
      </template>
    </dom-module>

Default text values are immediately extracted from the embedded JSON without overheads of run-time traversal into the whole template.