⚡ React Internals: Virtual DOM 🖼️ vs Fiber Node 🔗 for Performance Explained

Learn how React leverages Virtual DOM and Fiber Node to efficiently update your UI and keep apps smooth. ✨

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When I first started diving deep into React, I kept wondering: “Are Virtual DOM and Fiber Node the same thing?” 🤔
The short answer is no, but they are closely related, like two teammates ⚽ with different roles in a match.

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🔹 Are They the Same? What’s the Relation? 🧩

• Virtual DOM (VDOM) 🖼️: a snapshot of your UI in memory.
• Fiber Node 🔗: the task manager for React, tracking updates to each component individually.

How they work together:

1. When state or props change, React creates a new Virtual DOM tree 🌳
2. React diffs the new VDOM with the previous VDOM 🔍 to detect changes
3. Each detected change is represented as a Fiber Node (unit of work) ✂️
4. Fiber schedules these updates incrementally on the main thread, deciding what to prioritize, pause, or resume 🕒
5. The real DOM is updated smoothly without blocking the UI 🏗️

In short:

• VDOM calculates what to update
• Fiber decides how and when to update ⚡

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🔹 Virtual DOM 🖼️

The Virtual DOM is an in-memory representation of the real DOM. React updates this virtual copy first, instead of touching the browser DOM directly.

How It Works:

1. Render the UI to a Virtual DOM tree 🌳
2. On state/props update, create a new Virtual DOM tree 🔄
3. Diff the old and new VDOM to find changes 🔍
4. Patch only the changed parts to the real DOM 🏗️

Pros:

• ⚡ Performance optimization – fewer direct DOM updates
• 🖌️ Declarative UI – React computes changes abstractly
• 🧠 Easier to reason about state updates and re-rendering

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🔹 Fiber Node 🔗

Fiber is React’s reconciliation engine introduced in React 16.
Each component corresponds to a Fiber Node, a unit of work storing metadata like:

• 🏷️ Component type
• 📝 Props and state
• 🔗 Parent, child, sibling pointers
• ⚠️ Effect tags (tracking updates)

Why Fiber?

Previously, React’s diffing blocked the main thread ⏳ for large trees. Fiber solves this by:

• Splitting updates into small units ✂️
• Prioritizing important updates (animations vs background tasks) 🎯
• Pausing, aborting, or resuming work for smooth UIs 🛑➡️▶️

Example Fiber Tree:

App
├─ Header
│  └─ Logo
├─ Content
│  ├─ Article
│  └─ Sidebar
└─ Footer

Each node is a Fiber Node, with links to parent, child, and sibling Fibers 🔗.

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🔹 Virtual DOM vs Fiber: Key Differences ⚔️

Feature	Virtual DOM 🖼️	Fiber Node 🔗
Purpose	Represents UI in memory	Unit of work for incremental rendering
Updates	Synchronous diff & patch	Can be split, prioritized, paused, resumed
Performance	Reduces unnecessary DOM updates	Optimizes updates with scheduling ⚡
Data Stored	Tree of React elements	Props, state, effect tags, pointers
Granularity	Whole tree diff	Node-level, fine-grained control 🧩

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🔹 TL;DR Story 📖

I once faced a laggy React app 🐌 with heavy nested components. Using just the Virtual DOM was fine for small apps, but with hundreds of updates, the UI stuttered. Fiber’s incremental reconciliation saved the day 🎉, letting React pause low-priority updates and keep animations smooth.

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🔹 Conclusion ✅

• Virtual DOM 🖼️: Represents what the UI should look like at a given moment. It’s just a snapshot of the UI—no knowledge of how to update it incrementally.

• Fiber Node 🔗:Is a unit of work associated with a VDOM node. It keeps track of state, props, effects, and links to parent/child/sibling nodes, and tells React how, when, and in what order to update the real DOM.

• Together: VDOM calculates changes → Fiber schedules updates efficiently ⚡

This duo is why React can remain both declarative and high-performance, even in large apps.

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Author: Yogesh Bamanier
LinkedIn: https://www.linkedin.com/in/yogesh-007/