StackOverflow answer

http://stackoverflow.com/questions/8588041/ember-js-handlebars-custom-helper/8687459#8687459

by ud3323

HTML

<script src="http://cloud.github.com/downloads/emberjs/ember.js/ember-0.9.3.js"></script>
<script type="text/x-handlebars">
  {{#view Ember.View currentBusinessBinding="App.businessController.business"}}
    {{#view App.StateView stateName="test1"}}
      <p>Test 1</p>
    {{/view}}

    {{#view App.StateView stateName="test2"}}
      <p>{{parentView.currentBusiness.state}}</p>
    {{/view}}
  {{/view}}
</script>

JavaScript

window.App = Ember.Application.create();

App.businessController = Ember.Object.create({
    business: Ember.Object.create({
        state: 'test1'
    })
});

App.StateView = Ember.View.extend({
    isVisible: function() {
        return this.get('stateName') === this.getPath('parentView.currentBusiness.state');
    }.property('parentView.currentBusiness.state')
});

setTimeout(function() {
    App.businessController.business.set('state', 'test2');
}, 3000);