Do you have experience working with modern frontend frameworks (Vue, React, Svelte)? What is reactivity and how is it implemented in React?

Yes, I have experience working with modern frontend frameworks, particularly React and Vue.

Reactivity is a concept where the interface automatically updates when data changes. In React, reactivity is implemented through state and props. When the component's state changes using the setState function or hooks, React re-renders the component, updating the virtual DOM and then synchronizing the changes with the real DOM.

Example with React hook useState:

import React, { useState } from 'react';

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

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

Here, when setCount is called, React understands that the state has changed and automatically updates the interface.