`observerRemovedNode` called when `element.parentNode` is `null` leads to crash

[louwers]

Not sure when exactly this can happen. I see it with bau.loop. requestAnimationFrame is unreliable, an element could have been added to the DOM, or it could not have.

@FredericHeem Do you have ideas here? Looked at it for a while but could not come up with a fix.

[louwers]

Maybe a global MutationObserver that calls bauMounted and bauUnmounted, using a weak map from elements to those functions.

[louwers]

Here is a very simple reproduction that makes observerRemovedNode crash.

/** @import * as t from '/pages/pages-types.ts' */

/** @type {t.Component} */
function MyComponent({bau}) {
  const { div } = bau.tags;
  const state = bau.state([]);

  state.val.push(1);

  return bau.bind({
    deps: [state],
    render: () => (data) => {
      return div(
        {
          bauUnmounted: () => {}
        },
        data.length)
    }
  })
}

/** @type {t.Page} */
export default function Page(props) {
  // const { bau } = props;
  return MyComponent(props)
}

[FredericHeem]

Is this the following error ?

bau.js:356 Uncaught TypeError: Failed to execute 'observe' on 'MutationObserver': parameter 1 is not of type 'Node'.
    at observerRemovedNode (bau.js:356:8)
    at bau.js:426:13

[louwers]

@FredericHeem Yep, it's because it's not mounted yet so it doesn't have a parent yet.

[FredericHeem]

should be fixed by #156

[louwers]

@FredericHeem I don't think that is a correct fix. bauUnmounted will never be called if this problem is triggered due to a timing issue. I think if bauMounted is called, then it should be guaranteed that bauUnmounted gets called.

[FredericHeem]

It seems that the element was never mounted in the first place. In the example, 2 renders occur, first with bau.state([]), second render state.val.push(1).

[louwers]

Yes ideally bauMounted is called and the MutationObserver for bauUnmounted is set up when the component is actually mounted, without relying on requestAnimationFrame.

[FredericHeem]

yes indeed, fixed in #158

[louwers]

Nice!

One critical issue though bauUnmounted will never get called if bauMounted is not set.

I have identified another problem with the current implementation, but I think it is a different issue: #159

[FredericHeem]

Indeed, this is done in #161

[louwers]

Nice one!