What is the difference between "UI tree" and "render tree" in the docs?

[smikitky]

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Recently an article called "Your UI as a Tree" has been added, introducing a new concept called "render tree". However, the React docs have been using a similar term, "UI tree", such as in the article "Preserving and Resetting State" and "Passing Data Deeply with Context" where this term appears many times.

Are these exactly the same concept? Or are they different? Initially, I thought that they were the same concept, at least in the context of how React and ReactDOM work. But could they actually be different?

My current understanding is as follows:

• JSX tree: The nested JSX tag hierarchy that developers can return from a component.
• Render tree: The component hierarchy in a single pass of React rendering. This concept exists in the core React code, not ReactDOM. A new one is created for each render pass.
• DOM tree: The tree of browser DOM elements you can traverse with querySelectorAll(), etc.. Changes over time as a result of the commit.
• UI tree: ???

The question here is, "Is a render tree immutable?" According to "Your UI as a Tree", a render tree is an immutable data structure corresponding to a single render pass, like a snapshot of a specific render, traditionally referred to as "virtual DOM" or "(UI) description":

• A render tree represents a single render pass of a React application.
• Although render trees may differ across render passes, ...

It also equates the render tree and the UI tree:

• React creates a UI tree from your components.
• React creates a render tree, a UI tree, composed of the rendered components.

On the other hand, in "Preserving and Resetting State", it says, "React removed the Counter from the UI tree and destroyed its state". This seems to indicate that the UI tree is mutable, hence different from the render tree.

After reviewing the usage of "UI tree" throughout the documentation, my tentative conclusion is that "UI tree" has now become an ambiguous concept that may refer to either a render tree or a DOM tree depending on the context. Now that "render tree" is introduced and clearly defined, the term "UI tree" might be retired from most part of the documentation for the sake of consistency. What do you think?

I understand that such discussions are usually not much of an issue, but I don't want to see the problem of the legacy docs again, where consistency was lost as new articles were added. Once there's some consensus, I would like to create a PR to maintain consistency.

/CC @lunaleaps

[lunaleaps]

Hi @smikitky, that's a good callout that the UI tree mentions platform specific tags and yes these concepts aren't super well-defined and differentiated because their definitions are each motivated in explaining a concept. UI tree mentions are trying to explain state and the render tree docs I added were trying to illustrate parent/child relationships. As well, when the docs for "Preserving and Resetting State" were written, we were maybe less sensitive about trying to teach React concepts without anchoring to the web.

For UI trees, I think we could essentially say they're conceptually the same as a render tree (although I do think the terminology is less precise since we've also mentioned other non-React examples of UI trees). When we say "React removed the Counter from the UI tree" that could conceptually be mutability or a new tree with a new structure, the emphasis is more on the event of change. Both concepts, UI tree and render tree don't really exist in code.

Does that help? And for sure open to modifying some of these docs for consistency -- maybe we didn't need to go into detail so much on render docs re: conditional rendering and platform agnostic-ness and would be open to removing.