Bacon.js Bus.plug: error with impure: not observable: [object Object]

I tried to learn baconjs. https://baconjs.github.io/tutorials.html#content/tutorials/2_Ajax

But, I got an error in "Bus.plug"

var cart = ShoppingCarEt([])
var cartView = ShoppingCartView(cart.contentsProperty)
var newItemView = NewItemView()
cart.addBus.plug(newItemView.newItemStream)

      

        
        
        
      

    

Mistake:

Uncaught Error: not an Observable : [object Object]
shopBundle.js:145 assertObservable
shopBundle.js:2650 Bus.plug

      

        
        
        
      

    

I am using the following

• baconjs@0.7.53
• jquery@2.1.3
• bacon-jquery-bindings@0.2.8
• webpack 1.7.3

What am I doing wrong? Thank.

Edit: 2015/3/25

The reason is that newItemView.newItemStream is not being observed.
( newItemView.newItemStream instanceof Bacon.Observable

returns false.)

And newItemView.newItemStream is EventStream

EventStream {takeUntil: function, sampledBy: function, combine: function, flatMapLatest: function, fold: function…}

      

        
        
        
      

    

Are not all monitored events EventStream?

I made a newItemStream like this:

var $button = $('#addButton');
var $nameField = $('#nameText');
var newItemProperty = Bacon.$.textFieldValue($nameField);
var newItemClick = $button.asEventStream('click');
var newItemStream = newItemProperty.sampledBy(newItemClick);

      

        
        
        
      

    

The following works great. It was my mistake on the first question.

/ * And I try simpler code. He has the same error. * /

 var someStream = Bacon.interval(1000).map(function() {
    return new Date().getTime();
});
var bus = new Bacon.Bus();
bus.log();
bus.plug(someStream);