app.js

Editor.ElementView = Em.View.extend({
  classNameBindings: ['isSelected'],

  isSelected: function() {
    var selectedElement = Editor.selectedElementController.get('content'),
        content = this.get('content');

    if(selectedElement === content) { return true; }
  }.property('Editor.selectedElementController.content', 'content'),

  click: function(){
    // Select this element on click
    Editor.selectedElementController.set('content', this.get('content'));
  }

});