behavior of hx-swap-oob if the target element does not exist

[untitaker]

consider the following demo:

index.html

<script src="https://unpkg.com/[email protected]"></script>

<h2 id=heading hx-swap-oob="true">main</h2>

<div style='border: red' hx-boost="true">
    <main>
        <a href="other.html">other</a>
    </main>
</div>

other.html

<script src="https://unpkg.com/[email protected]"></script>

<h2 id=heading hx-swap-oob="true">other</h2>

<div style='border: red' hx-boost="true">
    <main>
        <a href="index.html">main</a>

    </main>
</div>

I'd expect that clicking the link swaps out the h2 and link text accordingly, as hx-boost is set up to swap out the entire body.

instead clicking the boosted link makes the header disappear. after I remove hx-swap-oob, it works fine.

you might wonder why hx-swap-oob is present at all. that's because on another page I'm using hx-swap to instead of hx-boost to enable a more sophisticated replacement of content. I don't want to use conditions on the server to satisfy both usecases because that means the HTML fragment will be loaded and cached twice.

is this kind of thing possible at all? is there some fallback behavior for hx-swap-oob that would leave the element alone if a target ID can't be found in the parent page?

thanks in advance

[scrhartley]

I think oob swaps are done first:
so index.html has its heading's content replaced, and other.html would no longer have the hx-swap-oob element.
Then the main swap would occur, which targets body by default,
and that would be replaced with the remaining html from other.html, which has already has the hx-swap-oob element removed.

[untitaker]

Thank you, it seems that hx-target=main and hx-select=main solves this issue. I wish htmx would warn for this situation