Extracted from https://github.com/facebook/react/issues/12643.

We're currently diff a host node in the complete phase even if it has bailed out in the begin phase. By itself, this just means we're doing a little bit more work than necessary. But it also has some observable effects. In particular, https://github.com/facebook/react/issues/13424 (which by itself would be very rare and probably not worth fixing) is made worse because we end up committing update to inputs from another component.

I have a fix for this in https://github.com/facebook/react/pull/13423. Filing this for posterity.
state = {flip: false, count: 0};
        flip() {
          this.setState({flip: true, count: this.state.count + 1});
        }
        tick() {
          this.setState({count: this.state.count + 1});
        }
        render() {
          const useB = !this.props.forceA && this.state.flip;
          return <div onClick={useB ? handlerB : handlerA} />;
        }
      }
      class Click extends React.Component {