Morph within an animation frame

[joeldrapper]

No description provided.

[fractaledmind]

👍🏼

[midnightmonster]

I think in general the browser knows when it's executing JavaScript and doesn't need to be in a requestAnimationFrame callback to optimize renders, nor does using requestAnimationFrame guarantee that you or some other code won't do something that requires synchronous layout, which isn't painting as such but is still quite costly, so I'm not sure this particularly helps with performance—but it definitely changes the semantics of the code!

I.e., the work of myMorph.morph is now async with no guaranteed timeline and no explicit way to await its completion, so the actual morphing now happens at an arbitrary-ish time after any other synchronous code that's in execution order after myMorph.morph(). This means:

1. Previously, some other xhr event handlers could assume that the morph work will be done by the time they run, and now they cannot.
2. Multiple morphs (e.g. in phlex JS) called one after the other may fail in messy ways, as the DOM node against which a later morph was enqueued may not be part of the DOM anymore by the time it actually runs.

At a minimum, with morph being async, I would expect it to return a promise that's resolved once it's done (which would also simplify your tests).

[midnightmonster]

Summarizing further comments from Discord, separating the morphing from the identifying the nodes to be morphed introduces infinite race conditions: with this change, literally anything can happen to the page between the time someone calls morph(node, reference) and the time that we attempt to morph node with the new content from reference. It is also not possible for calling code to remove the risk of nodes changing or being queried between call and effect.

Bottom line: with this change reverted, it would still be trivial for calling code to morph within an animation frame callback if desired, but with this change retained, it is impossible to morph synchronously or race-safely.

This is irreconcilably incompatible with (at least) Idiomorph's behavior/API and is not a polite choice for an implement-an-algorithm library to make. The change should be reverted.

[joeldrapper]

Thanks for bringing this up. 🙏