How does virtual DOM in React work? What are its benefits and downsides?

TL;DR

The virtual DOM in React is a lightweight copy of the actual DOM. When the state of a component changes, React creates a new virtual DOM tree and compares it with the previous one using a process called "reconciliation." Only the differences are then updated in the actual DOM, making updates more efficient. The benefits include improved performance and a more declarative way to manage UI. However, it can add complexity and may not be as performant for very simple applications.

How does virtual DOM in React work?

What is the virtual DOM?

The virtual DOM is a concept where a virtual representation of the UI is kept in memory and synced with the real DOM by a library such as React. This process is called "reconciliation."

How does it work?

Initial render: When a React component is first rendered, a virtual DOM tree is created. This tree is a lightweight copy of the actual DOM.
State change: When the state of a component changes, React creates a new virtual DOM tree.
Diffing: React compares the new virtual DOM tree with the previous one to find the differences. This process is known as "diffing."
Reconciliation: React updates only the parts of the actual DOM that have changed, based on the differences found during the diffing process.

Code example

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <p>{this.state.count}</p>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

In this example, when the button is clicked, the state changes, triggering a new virtual DOM tree to be created. React then compares this new tree with the previous one and updates only the <p> element in the actual DOM.

Benefits of virtual DOM

Improved performance

Efficient updates: By updating only the parts of the DOM that have changed, React minimizes the number of costly DOM operations.
Batch updates: React can batch multiple updates together, reducing the number of re-renders.

Declarative UI

Simplified development: Developers can describe what the UI should look like for a given state, and React takes care of updating the DOM to match that state.

Cross-platform

React Native: The virtual DOM concept allows React to be used for mobile app development with React Native, providing a consistent development experience across platforms.

Downsides of virtual DOM

Complexity

Learning curve: Understanding how the virtual DOM works and how to optimize components can be challenging for beginners.
Overhead: For very simple applications, the overhead of maintaining a virtual DOM may not be justified.

Performance limitations

Not a silver bullet: While the virtual DOM improves performance for many use cases, it may not be as performant as manual DOM manipulation for very specific, highly optimized scenarios.

How does virtual DOM in React work? What are its benefits and downsides?

TL;DR