Ember-Meta module. See first comment for usage etc.!

ember-meta.js

// include this code in your application, you don't need to call any initialization manually!

Ember.Application.initializer({
  name: "meta",

  initialize: function(container, application) {
    // helper function to get tag from dom
    var _getTag = function(tagname, property, value) {
      var tags = document.head.getElementsByTagName(tagname),
        tag,
        i;
      for (i = 0; i < tags.length; i++) {
        tag = tags[i];
        if (tag[property] && tag[property] === value) {
          return tag;
        }
      }
    };

    // hold logic and information
    var Meta = Ember.Object.extend(Ember.Evented, {
      application: null,

      // string values
      title: null,
      description: null,

      // dom elements
      _ogTitle: null,
      _description: null,
      _ogDescription: null,

      // defaults
      defaults: {
        title: null,
        description: null
      },

      summary: Ember.computed(function() {
        return '<title>' + this.get('title') + '</title>\n' +
          this.get('_ogTitle').outerHTML + '\n' +
          this.get('_description').outerHTML + '\n' +
          this.get('_ogDescription').outerHTML;
      }).property('_ogTitle', '_ogDescription'),

      // propagate changes to dom elements
      titleChanged: function() {
        document.title = this.get('title');
        this.get('_ogTitle').setAttribute('content', this.get('title'));
        this.notifyPropertyChange('_ogTitle');
      }.observes('title'),

      descriptionChanged: Ember.observer(function() {
        this.get('_description').setAttribute('content', this.get('description'));
        this.get('_ogDescription').setAttribute('content', this.get('description'));
        this.notifyPropertyChange('_ogDescription');
      }, 'description'),

      init: function() {
        this._super();
        this.on('reloadDataFromRoutes', this.reloadDataFromRoutes);
      },

      reloadDataFromRoutes: function() {
        var handlers = this.get('application').Router.router.currentHandlerInfos,
          newTitle,
          newDescription,
          i = handlers.length;
        // walk through handlers until we have title and description
        // take the first ones that are not empty
        while (i--) {
          var handler = handlers[i].handler;
          if (!newTitle) {
            newTitle = Ember.get(handler, 'metaTitle');
          }
          if (!newDescription) {
            newDescription = Ember.get(handler, 'metaDescription');
          }
        }
        // save changes or snap back to defaults
        if (newTitle) {
          this.set('title', newTitle);
        } else if (this.get('defaults.title')) {
          this.set('title', this.get('defaults.title'));
        }
        if (newDescription) {
          this.set('description', newDescription);
        } else if (this.get('defaults.description')) {
          this.set('description', this.get('defaults.description'));
        }
        this.trigger('didReloadDataFromRoutes');
      }
    });
    var meta = Meta.create({application: application});

    meta.set('defaults.title', document.title);

    // setup meta object
    // are there any tags present yet? if not, create them
    // ogTitle
    var _ogTitle = _getTag('meta', 'property', 'og:title');
    if (!_ogTitle) {
      _ogTitle = document.createElement('meta');
      _ogTitle.setAttribute('property', 'og:title');
      document.head.appendChild(_ogTitle);
    }
    meta.set('_ogTitle', _ogTitle);

    // description
    var _description = _getTag('meta', 'name', 'description');
    if (!_description) {
      _description = document.createElement('meta');
      _description.setAttribute('name', 'description');
      document.head.appendChild(_description);
    } else {
      meta.set('defaults.description', _description.content);
    }
    meta.set('_description', _description);

    // ogDescription
    var _ogDescription = _getTag('meta', 'property', 'og:description');
    if (!_ogDescription) {
      _ogDescription = document.createElement('meta');
      _ogDescription.setAttribute('property', 'og:description');
      document.head.appendChild(_ogDescription);
    } else {
      meta.set('defaults.description', _ogDescription.content);
    }
    meta.set('_ogDescription', _ogDescription);

    // save object to app
    application.set('meta', meta);
  }
});

router.js

// to update the information, a little push is required.
// you usually would want to do it like this:
App.Router.reopen({
  didTransition: function(infos) {
    this._super(infos);
    Ember.run.next(function() {
      // the meta module will now go trough the routes and look for data
      App.meta.trigger('reloadDataFromRoutes');
    });
  }
});

// as you can see, there is a App.meta object that handles all the action
// you can even set title and description directly if you want to!
App.meta.set('title', 'New Site Title');
App.meta.set('description', 'Somethign changed, so I update my meta data.');

// you can as well ask for all the tags that were set by calling
App.meta.get('summary');

routes.js

// you can define static metadata in your root url
App.BlogRoute = Ember.Route.extend({
  metaTitle: "My awesome blog",
  metaDescription: "Here you can read stuff from brushing my teeths to drying my hair."
});

// or dynamic metadata for dynamic routes
App.PostRoute = Ember.Route.extend({
  model: function(params) {
    // ... etc
  },
  
  metaTitle: function() {
    return this.get('context.title');
  }.property('context.title'),
  
  metaDescription: function() {
    return this.get('context.abstract');
  }.property('context.abstract')
});

// unfortunately, it's not possible to do metaTitleBinding: 'context.title' :(

@iStefo Very cool. Thanks for sharing this! I tested it on our app, but I ran into an issue. In my case, the _getTag function does not work properly. It seems the tag objects returned by getElementsByTagName are different from what you expect. There is an "attributes" indirection (e.g. tag.attributes[property]). I had to replace:

if (tag[property] && tag[property] === value) { ...

with

if (tag.attributes[property] && tag.attributes[property].value.toLowerCase() === value.toLowerCase()){ ...

I haven't tested thoroughly though, but I wanted to mention this to you in case you know what's going on.

But thanks again, great stuff!
PJ

Hi guys forget the ignorance here but I'm new to Ember, trying to make this work but getting App is undefined when calling App.meta.trigger('reloadDataFromRoutes'); inside my router. Thanks in advance