React’s efficiency comes from three key concepts: the **Virtual DOM**, **Diffing**, and **Reconciliation**.


**What is the Virtual DOM?**

The **Virtual DOM** in React is a lightweight JavaScript representation of the actual DOM. It allows React to efficiently update the UI by comparing the current Virtual DOM with a previous version and applying only the necessary changes to the real DOM.

```js
const virtualDOM = {
  type: 'div',
  props: {
    id: 'container',
    children: [
      {
        type: 'h1',
        props: {
          children: 'Hello, Virtual DOM!'
        }
      },
      {
        type: 'ul',
        props: {
          children: [
            {
              type: 'li',
              props: {
                children: 'Item 1'
              }
            },
            {
              type: 'li',
              props: {
                children: 'Item 2'
              }
            }
          ]
        }
      }
    ]
  }
};
```

**What is Diffing?**

When a component's **state** or **props** change, React **re-renders** it by creating a **new Virtual DOM tree**.
It then uses a process called **diffing** to compare the new Virtual DOM with the previous one.

The **diffing algorithm** efficiently detects the **smallest set of changes** needed to update  the real DOM, ensuring fast and optimized UI updates.

**What is Reconciliation?**

**Reconciliation** is the overall **process** React uses to update the UI in response to data changes:

- rendering components to a new Virtual DOM
- running the diffing algorithm
- Applying the minimal updates to the real DOM


Virtual DOM, Diffing & Reconciliation

How React uses the Virtual DOM, diffing algorithm, and reconciliation process to efficiently update the user interface.