Can React be considered a reactive library, and how does it implement reactivity?

React can be considered a reactive library in the sense that it responds to data changes and automatically updates the user interface. However, React does not implement reactivity in the traditional sense (like, for example, RxJS or Vue with reactive objects), but uses the concept of a virtual DOM and a unidirectional data flow.

When the component's state or props change, React triggers a re-rendering process of the virtual DOM, compares it with the previous version (diffing), and efficiently updates only the changed parts of the real DOM. Thus, reactivity is achieved through state management and re-rendering, not through automatic change tracking in data.

Example:

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

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

Here, when count changes, React automatically updates the display, which is a manifestation of reactivity in React.