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.
container,
    );
    expect(portalContainer.innerHTML).toBe('<div>portal:2</div>');
    expect(container.innerHTML).toBe('<div></div>');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(<p>portal:3</p>, portalContainer)}</div>,
      container,
    );
    expect(portalContainer.innerHTML).toBe('<p>portal:3</p>');
    expect(container.innerHTML).toBe('<div></div>');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(['Hi', 'Bye'], portalContainer)}</div>,
      container,
    );
    expect(portalContainer.innerHTML).toBe('HiBye');
    expect(container.innerHTML).toBe('<div></div>');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(['Bye', 'Hi'], portalContainer)}</div>,
      container,
    );
    expect(portalContainer.innerHTML).toBe('ByeHi');
    expect(container.innerHTML).toBe('<div></div>');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(null, portalContainer)}</div>,
      container,
    );
    expect(portalContainer.innerHTML).toBe('');
    expect(container.innerHTML).toBe('<div></div>');
  });
  it('should keep track of namespace across portals (simple)', () => {