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nicko
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Beginner
Asked: 2025-02-20T00:17:06+00:00 In:

What is the Virtual DOM and how does React use it?

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can you please explain this with an example?

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  1. Finn Phillips
    Beginner

    ⚡ What is the Virtual DOM in React?

    The Virtual DOM (VDOM) is an in-memory, lightweight representation of the actual DOM in your browser. React uses it to optimize UI rendering, ensuring updates are fast and efficient.

    ✅ 1️⃣ How the Virtual DOM Works:

    1. Initial Render:

      • React creates a Virtual DOM tree based on your component structure.
      • This virtual tree is then used to render the actual DOM in the browser.

    2. State/Prop Changes:

      • When state or props change, React creates a new Virtual DOM.
      • It doesn’t directly touch the real DOM right away.

    3. Diffing Algorithm:

      • React compares the new Virtual DOM with the previous one using its Reconciliation algorithm.
      • It identifies what has changed (this process is called “diffing”).

    4. Efficient Updates:

      • Only the parts of the actual DOM that changed are updated.
      • This minimizes expensive DOM manipulations, leading to faster performance.

    ⚡ 2️⃣ Virtual DOM vs Real DOM:

    Aspect Virtual DOM Real DOM
    Location Memory (in JavaScript) Browser
    Speed of Updates Fast (batch updates) Slow (direct updates)
    Re-rendering Selective (only changed elements) Full re-render (even if minor)
    Performance Optimized with diffing and batching Costly and time-consuming

    ✅ 3️⃣ React’s Virtual DOM Workflow:

    User Interaction (e.g., click, input)
    ↓
    React Updates State/Props
    ↓
    New Virtual DOM is Created
    ↓
    Diffing Algorithm (Compares New vs Old VDOM)
    ↓
    Minimal Updates Applied to Real DOM

    🛠️ 4️⃣ Example (With and Without VDOM):

    • Without Virtual DOM:
      Every time you type in an input field, the entire page might re-render.

    • With Virtual DOM (React):
      Only the specific input field updates — the rest of the page remains untouched.

    ⚡ 5️⃣ Why Is Virtual DOM Fast?

    1. Batch Updates:

      • React groups multiple changes and updates the DOM in a single pass.

    2. Minimized Reflows/Repaints:

      • Direct DOM manipulations can cause layout shifts (reflows/repaints), but the VDOM minimizes them.

    3. Asynchronous Rendering:

      • React 18’s Concurrent Mode allows certain updates to happen in the background, improving user experience.

    🔥 6️⃣ Real-World Benefit:

    Imagine an app with a dynamic list (e.g., a chat app). When a new message arrives:

    • Without VDOM: The entire list might re-render, causing flickers or lag.
    • With VDOM: Only the new message gets added, keeping the app smooth.

    💡 7️⃣ Bonus:

    • Frameworks like Vue.js also use a Virtual DOM.
    • But React’s diffing algorithm is highly optimized, making it lightweight and fast.