Generate alternate url for different locales so search engine could find them all.

src/js/app/index.js

@@ -1,6 +1,7 @@
 var Backbone = require('backbone');
 var EventEmitter = require('events').EventEmitter;
 var React = require('react');
+var _ = require('underscore');
 
 var assign = require('object-assign');
 var util = require('../util');
@@ -86,6 +87,22 @@ var vcsModeRefresh = function(eventData) {
   $('body').toggleClass('hgMode', !isGit);
 };
 
+var insertAlternateLinks = function(pageId) {
+  // For now pageId is null, which would link to the main page.
+  // In future if pageId is provided this method should link to a specific page
+
+  // The value of the hreflang attribute identifies the language (in ISO 639-1 format)
+  // and optionally a region (in ISO 3166-1 Alpha 2 format) of an alternate URL
+  var altLinks = _.map(LocaleStore.getSupportedLocales(), function(langCode) {
+    var url = "https://learngitbranching.js.org/?locale=" + langCode;
+    return '<link rel="alternate" hreflang="'+langCode+'" href="' + url +'" />';
+  });
+  var defaultUrl = "https://learngitbranching.js.org/?locale=" + LocaleStore.getDefaultLocale();
+  altLinks.push('<link rel="alternate" hreflang="x-default" href="' + defaultUrl +'" />');
+  $('head').prepend(altLinks);
+
+};
+
 var intlRefresh = function() {
   if (!window.$) { return; }
   $('span.intl-aware').each(function(i, el) {
@@ -249,6 +266,8 @@ var initDemo = function(sandbox) {
     tryLocaleDetect();
   }
 
+  insertAlternateLinks();
+
   if (params.command) {
     var command = unescape(params.command);
     sandbox.mainVis.customEvents.on('gitEngineReady', function() {
@@ -328,4 +347,3 @@ exports.getLevelDropdown = function() {
 };
 
 exports.init = init;
-

src/js/stores/LocaleStore.js

@@ -3,6 +3,7 @@
 var AppConstants = require('../constants/AppConstants');
 var AppDispatcher = require('../dispatcher/AppDispatcher');
 var EventEmitter = require('events').EventEmitter;
+var _ = require('underscore');
 
 var assign = require('object-assign');
 
@@ -30,6 +31,8 @@ var headerLocaleMap = {
   'pt-BR': 'pt_BR'
 };
 
+var supportedLocalesList = _.values(langLocaleMap).concat(_.values(headerLocaleMap));
+
 function _getLocaleFromHeader(langString) {
   var languages = langString.split(',');
   var desiredLocale;
@@ -73,6 +76,10 @@ AppConstants.StoreSubscribePrototype,
     return _locale;
   },
 
+  getSupportedLocales: function() {
+    return assign({}, supportedLocalesList);
+  },
+
   dispatchToken: AppDispatcher.register(function(payload) {
     var action = payload.action;
     var shouldInform = false;