What technology underpins React and what is it used for?

React is based on the technology Virtual DOM.

The Virtual DOM is an abstraction of the real DOM, representing a lightweight copy of the user interface structure in memory. React uses the Virtual DOM for efficient interface updates.

Why Virtual DOM is needed:

• When the component's state changes, React first updates the Virtual DOM.
• Then React compares the new Virtual DOM version with the previous one (this process is called "diffing").
• Based on the differences, React calculates the minimal set of changes needed to update the real DOM.
• This significantly reduces the number of operations on the real DOM, which are costly in terms of performance.

Thus, the Virtual DOM enhances the performance and responsiveness of React applications.

Example (simplified):

function Counter() {
  const [count, setCount] = React.useState(0);

  return (
    <div>
      <p>Counter: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increase</button>
    </div>
  );
}

When clicking the button, React updates the Virtual DOM, compares it with the previous state, and only changes the text in <p>, without re-rendering the entire DOM.