Diffing with real DOM is slow, majority of vdom libraries aren't diffing with real DOM. As an author of a "vdom" library, I don't like to think about "reconciler" as a diffing algorithm because it is a useless constraint, I like to think about it as a some kind of a VM that uses different heuristics to map state to different operations represented as a tree data structure.
> What I wonder is whether the reason for virtual DOM is really just historic, is there anything else that has caused its persistence other than inertia?
As a thought experiment try to imagine how would you implement such features:
- Declarative and simple API
- Stateful components with basic lifecycle like `onDispose()`
- Context API
- Components that can render multiple root DOM nodes or DOMless components
- Inside out rendering or at least inside out DOM mounting
- Conditional rendering/dynamic lists/fragments without marker DOM nodes
Here are just some basics that you will need to consider when building a full-featured and performant web UI library. I think that you are gonna be surprised by how many libraries that make a lot of claims about their performance or that "vdom is a pure overhead" are actually really bad when it comes to dealing with complex use cases.
I am not saying that "vdom" approach is the only efficient way to solve all this problems, or every "vdom" library is performant(majority of vdom libraries are also really bad with complex use cases), but it is not as simple as it looks :)
So thanks for listing out some concrete things that may be easier to implement with a virtual DOM. And if there are any other good resources out there, then do share! :)
Unfortunately there aren't any good resources on this topics. Everyone is just focusing on a diffing and unable to see a bigger picture. In the end, all feature-complete libraries implement diffing algorithms for dynamic children lists and attribute diffing for "spread attributes", so with this features we are kinda already implementing almost everything to work with DOM and create a vdom API, everything else are just slight optimizations to reduce diffing overhead. But working with DOM is only a part of a problem, it is also important how everything else is implemented, all this different features are going to be intertwined and we can end up with combinatorial explosion in complexity if we aren't careful enough. Svelte is a good example of a library that tried to optimize work with DOM nodes at the cost of everything else. As an experiment, I would recommend to take any library from this[1] benchmark that makes a lot of claims about its performance, and start making small modifications to the benchmark implementation by wrapping DOM nodes into separate components, add conditional rendering, add more dynamic bindings, etc and look how different features will affect its performance. Also, I'd recommend to run tests in a browser with ublock and grammarly extensions.
And again, it is possible to implement a library with a declarative API that avoids vDOM diffing and it will be faster that any "vdom" library in every possible use cases, but it shouldn't be done at the cost of everything else. But unfortunately, some authors of popular libraries are spreading a lot of misinformation about "vdom overhead" and even unable to compete with the fastest ones.
That's true, but you need to read a lot from the (V)DOM when diff'ing. Which was said to be slow with the read DOM. I don't know to which extent, and I've read it's not true anymore.
I don't think the diff'ing is done with the real DOM, but between two VDOMs. No?
Anyway, I personally find this approach heavy and like more how Svelte patches the DOM instead of computing a diff.