React is known for its fast and efficient UI updates — but what’s happening under the hood? 🧠
To truly harness the power of React, it’s crucial to understand how it renders components and reconciles changes behind the scenes. In this post, we’ll break down React’s Rendering & Reconciliation process step-by-step. Let’s dive in! 🚀
🔍 React’s Rendering & Reconciliation Process
🔹 1️⃣ Initial Render (Building the Virtual DOM)
- ✅ React starts by converting your components into a React Element Tree, also known as the Virtual DOM.
- ✅ This Virtual DOM is an in-memory representation of the actual DOM — a blueprint for what the UI should look like.
- ✅ React then builds a Fiber Tree from the Virtual DOM, which helps track updates and manage rendering efficiently.
🔹 2️⃣ State Update & Re-Render
- ✅ When state or props change, React invokes the component function again to generate a new Virtual DOM.
- ✅ React follows a top-down re-render approach — parent component changes affect all its children unless optimized.
- ✅ However, React doesn’t directly touch the real DOM yet. First, it figures out what actually changed.
🔹 3️⃣ Reconciliation (The Diffing Algorithm)
- ✅ React compares the new Virtual DOM with the previous Fiber Tree using its diffing algorithm.
- ✅ It creates a list of effects — updates, insertions, or deletions — needed to update the UI.
- ✅ This process is powered by the Fiber Reconciler, which allows React to pause, prioritize, and batch rendering efficiently.
🔹 4️⃣ Commit Phase (Final UI Update)
- ✅ React applies the changes to a Work-in-Progress (WIP) Fiber Tree.
- ✅ It then commits these updates to the actual DOM, batching them for better performance.
- ✅ DOM operations (like inserting, updating, or removing elements) are handled here in a highly optimized way.
🔹 5️⃣ UI Update & Browser Repaint
- ✅ Once the DOM is updated, the browser repaints the screen to reflect the new UI.
- ✅ The user sees the changes, and the app feels fast, smooth, and responsive.
🎯 Why Does This Matter?
Understanding React’s Fiber architecture and rendering lifecycle empowers us to:
- ✅ Avoid unnecessary re-renders.
- ✅ Write better-performing components.
- ✅ Debug rendering issues more effectively.
- ✅ Build scalable apps that stay fast as they grow.
By mastering React’s internal workings, we move beyond just writing code — we write smarter, faster code. 💡
🙌 Let’s Connect
I’d love to hear your thoughts, questions, or feedback.
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I’m always up for connecting with fellow frontend devs and React learners.
