Understanding the Virtual DOM in React

React is fast — but how is it so fast? One of the biggest reasons is the Virtual DOM.

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What is the DOM?

The DOM (Document Object Model) is a tree-like structure representing the HTML elements on a web page. Whenever you change something (like text or style), the DOM has to update, which can be slow if not handled properly.

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What is the Virtual DOM?

The Virtual DOM is a lightweight copy of the real DOM that React keeps in memory.

Instead of directly updating the real DOM every time something changes, React updates the Virtual DOM first, then compares it with the previous Virtual DOM (this process is called diffing). React then finds out what actually changed and updates only those parts of the real DOM.

This makes the whole process faster and more efficient.

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How React Uses Virtual DOM

Here's a simple breakdown:

1. You change the state or props in your component.
2. React creates a new Virtual DOM tree.
3. It compares the new Virtual DOM with the old one.
4. React finds the differences (called “diffing”).
5. React updates only the changed nodes in the real DOM.

This is much faster than re-rendering the entire DOM.

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Why is Virtual DOM Better?

Performance

React avoids unnecessary real DOM updates, which are expensive and slow.

Efficient Re-rendering

Only the parts of the UI that actually change get updated.

Smooth UI

Your app feels fast and responsive, even with many components.