i18n-msg/i18n-msg.html at master · benjaminpg/i18n-msg · GitHub

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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="observer.html">

<!-- Copyright Eric Bidelman <ebidel@gmail.com> -->

<!--
`<i18n-msg>` is a client-side solution for i18n message string replacement. It is modeled off the [Chrome extension i18n API](https://developer.chrome.com/extensions/i18n), which uses a `messages.json` file format.
The file contains localized strings for the language in question.

To set the language across your site, define `I18nMsg.lang` in your main page:

    document.addEventListener('HTMLImportsLoaded', function() {
      I18nMsg.lang = 'es';
      // I18nMsg.url = 'locales'; // optionally use custom folder for locales.
      Platform.performMicrotaskCheckpoint();
    });

<b>Note:</b> this is done in `HTMLImportsLoaded` so `I18nMsg` will be defined by
the time you set `I18nMsg.lang`. This timing is necessary under the polyfill and is
<b>not needed if the browser supports HTML Imports</b>, natively.

<b>Note:</b> you must call `Platform.performMicrotaskCheckpoint()` whenever
making a change to the `I18nMsg` object. This is required due to the removal
of `Object.observe()`.

### Message files

Setting a language instructs `<i18n-msg>` to read message ids from a predefined
file on your server. For example, `I18nMsg.lang = 'es'` will use `locales/es.json`.
`I18nMsg.lang = 'fr'` would use message strings from `locales/fr.json`.

The directory name can be configured by using the `messagesUrl` property, but the file
cannot. `<i18n-msg>` will always attempt to use messages from `<messagesUrl>/<LANG_YOU_SET>.json`.
You can also set and/or change this location globally, at any time, by setting `I18nMsg.url`.

<b>Example</b> - using a custom locales folder, setting it globally for all `<i18n-msg>` instances:

    I18nMsg.url = 'locales';

<b>Example</b> - set locales folder path on individual element:

    <i18n-msg messages-url="path/to/locales">fallback text</i18n-msg>

<b>Note:</b> message files are read once and reused for all instances of `<i18n-msg>`.

### Fallback text

If an appropriate message file can't be found, the `textContent` of the element is used as fallback text.

    <i18n-msg msgid="unknownmsgid">fallback text</i18n-msg>

### Placeholders

It's possible to insert text within the message which requires no translation (e.g: names, dates, numbers).
To make available the use of placeholders the message must contains $n (being n a numeric value) whenever a parameter
should be used, and to use these add the attribute "placeholders" and separate each parameter with ";;". Example:
JSON
    "textwithplaceholders" {
      "description" : "...",
      "message" : "I am $0 and I live in $1"
    }

HTML
    <i18-msg msgid="textwithplaceholders" paremeters="John Doe;;Seattle"></i18n-msg>

It's also possible to use {{}} and [[]] within the placeholders.

### Full example

    <html lang="es">
      ...
      <body>
        <p>"Days" in Spanish is <i18n-msg msgid="days">days</i18n-msg>!</p>
        <script>
          I18nMsg.lang = document.documentElement.lang || 'en';
        </script>
      </body>
    </html>

### Getting a message:

    // No argument returns the instance's message:
    document.querySelector('i18n-msg').getMsg();

    // Get a message by an id:
    document.querySelector('i18n-msg').getMsg('days');

@demo
-->
<dom-module id="i18n-msg"></dom-module>
<script>
(function () {

  window.I18nMsg = window.I18nMsg || {
    lang: null,
    url: 'locales',
    locales: {}
  };

  var _instances = []; // Holds all i18n-msg elements to have them easily updated with translation messages.
  var _fetching = false; // True if there's an outstanding XHR fetching a locale file.
  var _numInstancesUpdated = 0;

  Polymer({
    is: 'i18n-msg',

    /**
     * The `i18n-language-ready` is fired after the locale was fetched and all `<i18n-msg>` elements were updated.
     *
     * @event i18n-language-ready
     * @detail {{language: String}}
     */

    properties: {
      /**
       * The message id (key) for this message.
       */
      msgid: {
        type: String,
        value: null,
        observer: '_msgidChanged'
      },

      /**
       * Placeholders used to insert within the message if it contains replacement
       * patterns to switch with. To use this feature you must include the "placeholders"
       * attribute and use '' for the array and "" for each element.
       * Example: placeholders = '["John Doe","Seattle"]'
       */
      placeholders: {
        type: Array,
        value: [],
        observer: '_placeholdersChanged'
      },

      /**
       * The language being used.
       */
      language: {
        type: String,
        value: null,
        observer: '_languageChanged',
        readOnly: true
      },

      /**
       * The folder name where the localized `<lang>.json` files are located.
       * Overrides `window.I18nMsg.url` if not `null`.
       */
      messagesUrl: {
        type: String,
        value: 'locales'
      },

      /**
       * The message in the current locale
       */
      msg: {
        type: String,
        value: null,
        notify: true
      }
    },

    /**
     * An object containing the set of known language locales that have been loaded.
     */
    locales: {
      type: Object,
      value: I18nMsg.locales // static
    },

    ready: function() {
      this.messagesUrl = I18nMsg.url;
      this._setLanguage(I18nMsg.lang);

      // Have instances observe window.I18nMsg.lang changes
      // and go fetch the localized messages.json file.
      var observerLang = new PathObserver(window.I18nMsg, 'lang');
      observerLang.open(function(newValue, oldValue) {
        _numInstancesUpdated = 0;
        this._setLanguage(newValue);
      }.bind(this));

      // Have instances observe window.I18nMsg.url changes
      // and go fetch the localized messages.json file.
      var observerUrl = new PathObserver(window.I18nMsg, 'url');
      observerUrl.open(function(newValue, oldValue) {
        _numInstancesUpdated = 0;
        this.messagesUrl = newValue;

        // TODO: this will xhr the json file for each instance.
        // if (!this.language || _fetching) {
        //   return;
        // }

        this._fetchLanguage();
      }.bind(this));

      _instances.push(this);
    },

    attached: function() {
      var msg = this.getMsg(this.msgid)
      if (msg) {
        this.msg = msg;
        this.innerHTML = msg;
      }
    },

    /**
     * Returns a message in the current locale (set by `window.I18nMsg.lang`).
     * @method getMsg
     * @param {string=} opt_msgId Optional message id to lookup. If left off,
     * the instance's `msgid` property is used.
     * @return {string|null} Translated message or `null` if not found.
     */
    getMsg: function(opt_msgId) {
      var msgId = opt_msgId || this.msgid;
      var lang = this.locales[this.language];
      if (lang && lang[msgId]) {
        return lang[msgId].message;
      }
      return null;
    },

    _msgidChanged: function() {
      if (this.language && this.locales[this.language] && !_fetching && this.msgid) {
        this._updateElementMessage();
      }
    },

    _placeholdersChanged: function() {
      if (this.language && this.locales[this.language] && this.placeholders) {
        this._updateElementMessage(this);
      }
    },

    _languageChanged: function() {
      // Don't fetch .json file if it has already been
      // fetched or another instance is already trying to.
      if (this.language && this.locales[this.language] && !_fetching) {
        // Send one signal that language changed to outside.
        if (_numInstancesUpdated == _instances.length - 1) {
          this.fire('i18n-language-ready', {language: this.language});
        }

        this._updateElementMessage();
        _numInstancesUpdated++;

        return;
      } else if (!this.language || this.locales[this.language] || _fetching) {
        return;
      }

      this._fetchLanguage();
    },

    _fetchLanguage: function() {
      // if (_fetching) {
      //   return;
      // }

      _fetching = true;

      var url = /*this.baseURI + */this.messagesUrl + '/' + this.language + '.json';

      var xhr = new XMLHttpRequest();
      xhr.open('GET', url);
      xhr.onload = function(e) {
        _fetching = false;

        if (e.target.status !== 200 && e.target.status !== 0) {
          return;
        }

        var resp = JSON.parse(e.target.response);
        if (!this.msgid in resp) {
          console.warn(this.localName + ': "' + this.msgid + '" message id was not found in ' + url);
          return;
        }

        this.locales[this.language] = resp; // cache this locale.

        this._notifyInstances();

        this.fire('i18n-language-ready', {language: this.language});
      }.bind(this);
      xhr.onerror = function(e) {
        _fetching = false;
      };
      xhr.send();
    },

    _updateElementMessage: function(opt_instance) {
      var instance = opt_instance || this;

      var msg = instance.locales[instance.language][instance.msgid];
      if (msg && msg.message) {
        var message = msg.message;
        var placeholders = msg.placeholders;
        var phData = instance.placeholders;
        if ((placeholders) && (phData)) {
          var content, pos;
          for (var p in placeholders) {
            content = placeholders[p].content;
            if (content[0] == '$') {
              pos = content.substring(1, content.length);
              if (!isNaN(pos)) {
                content = (phData.length < pos) ? '' : phData[pos - 1];
              }
            }
            message = message.split('$' + p + '$').join(content);
          }
        }
        instance.msg = msg.message;
        instance.innerHTML = message;
      }
    },

    _notifyInstances: function() {
      for (var i = 0, instance; instance = _instances[i]; ++i) {
        instance._setLanguage(I18nMsg.lang);

        if (!instance.locales[instance.language][instance.msgid]) {
          console.warn(this.localName + ': "' + instance.msgid + '" message id was not found');
          continue;
        }

        this._updateElementMessage(instance);
      }
    }

  });

})();
</script>