Ember.js states

HTML

<script src="https://github.com/downloads/emberjs/ember.js/ember-0.9.3.js"></script>
<script type="text/x-handlebars">
    {{#each App.controller}}
        {{#view Em.View contentBinding="this"}}
            {{content}}
        {{/view}}
    {{else}}
        ELSE
    {{/each}}
</script>

JavaScript

App = Ember.Application.create({});

App.controller = Em.ArrayController.create({    
    content: [],
});

setTimeout(function(){
    App.controller.set('content', ["one", "two"]);
    setTimeout(function(){
        App.controller.set('content', []);
    },3000);
},3000);