We used to throw if event listener is not a function in Stack:

```js
ReactDOM.render(
  <h1 onClick={{}}>Hello World!</h1>,
  document.getElementById('container')
);
```

<img width="565" alt="screen shot 2017-08-08 at 3 41 08 pm" src="https://user-images.githubusercontent.com/810438/29077502-2646412e-7c50-11e7-8c99-3b7f6c0a2589.png">

Fiber silently ignores this.

I think we should throw. This would let us add support for objects (e.g. for passive listener configuration) if we want to in a minor rather than a major.
portalContainer3,
              ),
              <div key="e">portal1[1]</div>,
            ],
            portalContainer1,
          ),
          <div key="f">normal[1]</div>,
        ],
        container,
      );
      expect(portalContainer1.innerHTML).toBe(
        '<div>portal1[0]</div><div>portal1[1]</div>',
      );
      expect(portalContainer2.innerHTML).toBe('<div>portal2[0]</div>');
      expect(portalContainer3.innerHTML).toBe('<div>portal3[0]</div>');
      expect(container.innerHTML).toBe(
        '<div>normal[0]</div><div>normal[1]</div>',
      );
      ReactDOM.unmountComponentAtNode(container);
      expect(portalContainer1.innerHTML).toBe('');
      expect(portalContainer2.innerHTML).toBe('');
      expect(portalContainer3.innerHTML).toBe('');
      expect(container.innerHTML).toBe('');
    });
    it('should reconcile portal children', () => {
      var portalContainer = document.createElement('div');
      ReactDOM.render(
        <div>
          {ReactDOM.unstable_createPortal(<div>portal:1</div>, portalContainer)}
        </div>,