Ember.PromiseProxyMixin Class packages/ember-runtime/lib/mixins/promise_proxy.js:36

var ObjectPromiseProxy = Ember.ObjectProxy.extend(Ember.PromiseProxyMixin);

var proxy = ObjectPromiseProxy.create({
  promise: $.getJSON('/some/remote/data.json')
});

proxy.then(function(json){
   // the json
}, function(reason) {
   // the reason why you have no json
});

proxy.get('isPending')   //=> true
proxy.get('isSettled')  //=> false
proxy.get('isRejected')  //=> false
proxy.get('isFulfilled') //=> false

proxy.get('isPending')   //=> false
proxy.get('isSettled')   //=> true
proxy.get('isRejected')  //=> false
proxy.get('isFulfilled') //=> true

// Assuming the following json:
{
  firstName: 'Stefan',
  lastName: 'Penner'
}

// both properties will accessible on the proxy
proxy.get('firstName') //=> 'Stefan'
proxy.get('lastName')  //=> 'Penner'