🧩 Incremental DOM in Angular vs Virtual DOM in React — Let’s Decode the Difference

If you’re coming from a React background or just exploring Angular's internals, you’ve probably heard terms like Virtual DOM and Incremental DOM thrown around.

Let’s break it down—not just what they are, but how they work, why they exist, and what it means for performance and memory.

⚛️ Virtual DOM (React)

React uses a Virtual DOM as a way to optimize UI updates. Here’s how it works:

1. When your app’s state or props change, React re-renders the entire component tree (or a portion of it).
2. This rendering generates a new Virtual DOM tree (an in-memory representation of the real DOM).
3. React then performs a diffing algorithm between the old Virtual DOM and the new one.
4. Once the differences are known, React applies batched updates to the real DOM efficiently.

🧠 Benefits:

• Developer-friendly: you can just update state, and React figures out what to change.
• Minimizes DOM manipulations by doing a diff before updating.

💾 Downsides:

• Requires maintaining two trees in memory (old and new virtual DOM).
• Frequent re-renders can still have a performance cost in large trees.
• Abstracts away the DOM update process, which can sometimes lead to over-rendering if not optimized.

🅰️ Incremental DOM (Angular)

Angular (as of Ivy) takes a different route. Instead of creating and comparing trees, Angular compiles templates into a series of low-level DOM instructions. Here's how Incremental DOM works:

1. Templates are compiled into imperative code that knows exactly how to construct and update the DOM.
2. When change detection runs, Angular revisits the template instructions, and updates are made in-place in the real DOM.
3. No virtual DOM tree is created or stored. Instead, DOM updates are incremental and deterministic.

🔍 Think of it like this: While React says, “Let me recreate the UI in memory and compare,” Angular says, “I know exactly what needs to change, and I’ll update it directly.”

✅ Benefits:

• Lower memory usage: no extra trees, no diffing overhead.
• Faster first render: Angular renders directly using instructions.
• Smaller bundle size: Ivy generates tree-shakable code per component.
• Great for performance-critical, large-scale apps (common in enterprise).

💾 Downsides:

• Less flexible for advanced diffing scenarios (React’s reconciliation is more dynamic).
• Updates happen synchronously and are tied to Angular's change detection mechanism.

🧠 So, why did Angular choose Incremental DOM?

Angular targets enterprise-grade applications where predictability, memory efficiency, and scalability are crucial. Incremental DOM aligns well with Angular’s template-first philosophy, giving:

• More control over rendering.
• Better performance on mobile and low-memory devices.
• Faster compile time with Ivy and better optimization with tree-shaking.

🎯 If you’re building a complex SPA with Angular, know that the Incremental DOM is doing some seriously smart optimizations under the hood. It’s one of the reasons Angular apps scale so well in enterprise environments.

👇 I’d love to hear your thoughts. Have you experienced the differences firsthand between these two approaches? What impact did it have on your project?

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