[joesb]

Why is it relevant? The point is you are not the one needing to remember.

One day React could change from using Virtual Dom to the Svelte way and most user of library wouldn't notice.

The point of the article is that React remember where to make the modification for you.

[kreetx]

It seems like it's a non-effective way of doing it. In large DOM trees you need to manually interfere to make them update fast because (1) building even the virtual DOM and (2) then comparing this to the real DOM become slow => i.e the "React way" doesn't actually scale. Perhaps for a product guy this doesn't matter, but for an engineer it just feels wrong. Why not solve the real problem?

[lukevp]

Because the real DOM exists in a separate world where you have to cross a trust boundary. The vdom is an implementation detail of React because the real DOM is too slow to traverse to diff on every render. Think of it like this.. jquery is a wrapper around a querying API, so it’s like running a sql query that can be indexed in a b-tree or a hash map, because you query by id or class or some other attribute. React on the other hand needs the entire state, which is equivalent to a select *.

If you say why does react need the whole state, it’s because React is a translation layer between an immediate mode representation and a retained mode system (the DOM). To illustrate this in a basic way, think of a checkbox. It is an entity in the DOM, but it is also retaining state itself (there is a Checked property that persists as long as it is set, so you know it has state). The only way to know if that checkbox is checked or not is to query the DOM to get the checkbox entity, or to “control” the rendering of the component so you can always derive the checked state from somewhere in your code, and force its state to match. React controlled components are a way to express unidirectional state from your code to the UI.

What situation were you in where vdom was the problem? I’d love to see an example. It is likely that vdom was not the performance issue, something was wrong with the implementation and causing a full re-render. Could you link a sandbox?

[kreetx]

I understand why it's convenient to derive the UI from the state, no need to explain that.

But what react does is: for any change in state it creates the entire virtual DOM" regardless of if there was a single checkbox change and everything else remained the same. Then it compares this whole tree* to the real DOM, and then only replaces the parts that changed. The "win" of react is that instead of rendering the entire real DOM again and again it just renders something that is not seen and then swaps out the changed parts in the real DOM.

Why not short-circuit from changes in state to real DOM instead?

I think any google sheet like app would do: you type into some box, this changes state which triggers the creation of the virtual DOM for the entire sheet. Then it compares this entire sheet to the real DOM, finds that only one cell has changed and swaps that out. There will be one entire virtual DOM per character typed. Which is why I'd presume most if not all such applications need to add custom code (using `shouldComponentUpdate`) to fix this scaling issue.