Virtual DOM vs Real DOM: Key Differences and When to Use Each

The Real DOM is the actual web page structure that browsers render, while the Virtual DOM is a lightweight copy React uses to efficiently update the UI. React updates the Virtual DOM first, then compares it to the Real DOM to apply only necessary changes, improving performance.

Quick Comparison

Here is a quick side-by-side comparison of Virtual DOM and Real DOM to understand their main differences.

Factor	Virtual DOM	Real DOM
Definition	A lightweight JavaScript copy of the Real DOM	The actual DOM rendered by the browser
Update Speed	Faster because it updates in memory	Slower because it updates the browser UI directly
Manipulation	React updates Virtual DOM first	Direct manipulation causes reflow and repaint
Performance	Improves performance by minimizing real DOM changes	Can be slow with frequent updates
Use Case	Used internally by React for efficient UI updates	Used by browsers to display the page
Complexity	Abstracts DOM manipulation for developers	Requires manual DOM handling in vanilla JS

Key Differences

The Real DOM is the actual structure of the webpage that browsers use to display content. When you change something in the Real DOM, the browser has to recalculate styles, layout, and repaint the page, which can be slow if done often.

The Virtual DOM is a concept used by React where it keeps a copy of the Real DOM in memory as a JavaScript object. When the UI changes, React updates this Virtual DOM first, then compares it with the previous version to find exactly what changed. This process is called diffing.

After diffing, React updates only the parts of the Real DOM that actually changed. This selective update reduces the number of expensive operations on the Real DOM, making UI updates faster and smoother.

Code Comparison

This example shows how you might update a list of items by directly manipulating the Real DOM in plain JavaScript.

javascript

const list = document.getElementById('list');

function addItem(item) {
  const li = document.createElement('li');
  li.textContent = item;
  list.appendChild(li);
}

addItem('Apple');
addItem('Banana');

Output

<ul id="list"><li>Apple</li><li>Banana</li></ul>

Virtual DOM Equivalent

Here is how React uses the Virtual DOM to update the same list efficiently.

jsx

import React, { useState } from 'react';

function FruitList() {
  const [items, setItems] = useState([]);

  function addItem(item) {
    setItems(prevItems => [...prevItems, item]);
  }

  return (
    <>
      <button onClick={() => addItem('Apple')}>Add Apple</button>
      <button onClick={() => addItem('Banana')}>Add Banana</button>
      <ul>
        {items.map((item, index) => <li key={index}>{item}</li>)}
      </ul>
    </>
  );
}

Output

Buttons labeled 'Add Apple' and 'Add Banana' with an empty list below; clicking buttons adds items to the list dynamically.

When to Use Which

Choose Virtual DOM when building interactive web apps with React because it optimizes UI updates and improves performance automatically. It handles complex UI changes efficiently without manual DOM manipulation.

Use direct Real DOM manipulation only for very simple or small scripts where performance is not critical, or when working outside React. For modern web apps, relying on Virtual DOM through React is the best practice.

Key Takeaways

Virtual DOM is a fast, in-memory copy of the Real DOM used by React to optimize updates.

Real DOM updates are slower because they cause browser reflows and repaints.

React compares Virtual DOM versions to update only changed parts of the Real DOM.

Use Virtual DOM with React for better performance and simpler UI code.

Direct Real DOM manipulation is simpler but less efficient for complex apps.