Preact: Rendering components with identical children into the same parent container breaks

[hatched]

If you try to render two different components into the same parent container multiple times with shared child components the browser will throw an error:

Uncaught HierarchyRequestError: Failed to execute 'replaceChild' on 'Node': The new child element contains the parent.

"preact": "4.6.2",
"preact-render-to-string": "2.4.0"

Chrome Version 50.0.2661.75 (64-bit)

This is easier to explain with some code:

class Intro extends Component {
  render(props) {
    return (<span>Hello</span>)
  }
}

class Index extends Component {
  render(props) {
    return (
      <div>
        <Intro />
      </div>)
  }
}

class Join extends Component {
  render(props) {
    return (<Intro />)
  }
}

  let components = [Index, Join, Index, Join, Index]
  // This loop simulates the user navigating forward and backwards over two components.
  components.forEach(function(Cmp) {
    render(
      <Cmp data={window.preactProps} />,
      document.body,
      document.body.firstChild)
  })

[developit]

Ah - looks like this has to do with one of the components being high-order and the other not.

[developit]

@hatched Quick fix for this (at least for your example) would be to not rely on document.body.firstChild. (interesting to note: using document.body.lastChild seems to fix the issue above).

Instead, I'd recommend using the returned root node from render():

  let root;
  let components = [Index, Join, Index, Join, Index]
  // This loop simulates the user navigating forward and backwards over two components.
  components.forEach(function(Cmp) {
    root = render(
      <Cmp data={window.preactProps} />,
      document.body,
      root)
  })

This accounts for the case where render() destroys the previous rendered root.

I'm working on a lower-level fix for this, in case the explanation above only solves your reproduction and not the bug as you ran into it (let me know).

[hatched]

Thanks for the quick reply!

Because this is being first rendered on the server I had to initialize root with document.body.firstChild so that it wouldn't get a duplicate render on load. With that change it appears to have resolved the issue.

function renderParent(Component) {
  let root = document.body.firstChild
  root = render(
    <Component data={window.preactProps} />,
    document.body,
    root)
}

[developit]

Perfect. Now I'm a little stuck: should I keep the fix I just added that checks before invoking replaceChild(), or drop it since it still doesn't fix the firstChild issue?

[hatched]

I think that it is always a good idea to code defensively and it is a quite small change so unless there are some unintended consequences that I'm not aware of I'd vote to keep it in.

[developit]

True, it's literally 2 bytes after gzip. I shouldn't agonize over these things so much, haha.

[developit]

I'm going to close this issue out for now since we've got a solution, though I'll likely re-reference it when I address making render() automatically detect and attach to existing rendered components.

_edit:_ for reference, reproduction I was using to test: http://jsfiddle.net/developit/t8p15pps/