Simple starting point for Ember.js fiddles

HTML

<script src="https://github.com/downloads/emberjs/ember.js/ember-0.9.5.js"></script>
<script type="text/x-handlebars" >
</script>

JavaScript

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

App.Parent = Ember.Object.extend({
    foo: 'someValue',
    child: null,
    setParentOnChild: function() {
        var child = this.get('child');
        if (child) {
            child.set('parent', this);
        }
    }.observes('child'),
    init: function() {
        this.setParentOnChild();
    }
});

App.Child = Ember.Object.extend({
    init: function() {
        this._super();
        // you can't access your parent here
        // but you can subsequent to assigning
        // the object to a parent instance
    },
    log: function() {
        var p = this.get('parent')
        console.log("I am " + this.toString() + ". My parent's 'foo' is '" + p.get('foo') + "'");
    }
});

console.log("Creating a parent with a child.");
p = App.Parent.create({
    foo: 'some other value',
    child: App.Child.create()
});
p.get('child').log();

console.log("Setting a new child on the parent.");
p.set('child', App.Child.create());
p.get('child').log();