dodrio is an experimental virtual DOM library for Rust and WebAssembly. It
is a proving ground for a bump allocation-based virtual DOM architecture, that I
believe is the best way to take advantage of WebAssembly's strengths in the
context of a virtual DOM library.
I reiterate that dodrio is in a very experimental state. It has not
actually been profiled or tuned for performance yet, so while I think the design
should yield a very fast virtual DOM library, dodrio is almost certainly not
fast right now. Additionally, it is probably riddled with bugs, and is assuredly
missing features that are critical for actually building Web applications.
Bump allocation is essentially the fastest method of allocating objects. It has constraints, but works particularly well when allocation lifetimes match program phases. And virtual DOMs are very phase oriented.
dodrio maintains three bump allocation arenas:
- The newest, most up-to-date virtual DOM. The virtual DOM nodes themselves and any temporary containers needed while creating them are allocated into this arena.
- The previous virtual DOM. This reflects the current state of the physical DOM.
- The difference between (1) and (2). This is a sequence of DOM mutation operations — colloquially known as a "change list" — which if applied to the physical DOM, will make the physical DOM match (1).
Rendering happens as follows:
- The application state is rendered into bump allocation arena (1).
- (1) diffed with (2) and the changes are emitted into (3).
- JavaScript code applies the change list in (3) to the physical DOM.
- (1) and (2) are swapped, double-buffering style, and the new (1) has its bump allocation pointer reset, as does (3).
- Rinse and repeat.
The change list that represents the difference between how the physical DOM currently looks, and our ideal virtual DOM state is encoded in a tiny stack machine language. A stack machine works particularly well for applying DOM diffs, a task that is essentially a tree traversal.
dodrio is just a library. (And did I mention it is experimental?!) It is not a
full-fledged, complete, batteries-included solution for all frontend Web
development. And it never intends to become that either. Its highest ambition is
to prove that its bump allocation-based design is a good one, and maaaayyyyyybe
become a production-grade virtual DOM library that you could plug into a larger
application or toolkit eventually. But it will never be a complete,
batteries-included framework.