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.
render() {
          return <div style={{margin: '0'}} />;
        }
      }
      ReactTestUtils.renderIntoDocument(<Component />);
      expectDev(console.error.calls.count()).toBe(0);
    });
    it('should warn nicely about NaN in style', () => {
      spyOn(console, 'error');
      var style = {fontSize: NaN};
      var div = document.createElement('div');
      ReactDOM.render(<span style={style} />, div);
      ReactDOM.render(<span style={style} />, div);
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toEqual(
        'Warning: `NaN` is an invalid value for the `fontSize` css style property.',
      );
    });
    it('should update styles if initially null', () => {
      var styles = null;
      var container = document.createElement('div');
      ReactDOM.render(<div style={styles} />, container);
      var stubStyle = container.firstChild.style;
      styles = {display: 'block'};
      ReactDOM.render(<div style={styles} />, container);
      expect(stubStyle.display).toEqual('block');