Tell me about React, how deeply have you dealt with its internal nuances? What have you used?

React is a library for building UI based on a component approach and virtual DOM. I have worked with React at a middle level, using functional components with hooks (useState, useEffect, useMemo, useCallback) for state management and optimization.

Internal nuances I encountered include:

• Understanding how the virtual DOM and reconciliation work for rendering optimization.
• Features of hooks, such as rules of invocation and dependencies in useEffect.
• Context (React Context) for passing data without props.
• State management with Redux and middleware (redux-thunk).
• Performance optimization through component memoization (React.memo).

An example of using useEffect with cleanup:

import React, { useState, useEffect } from 'react';

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

  useEffect(() => {
    const id = setInterval(() => {
      setCount(c => c + 1);
    }, 1000);
    return () => clearInterval(id); // cleanup on unmount
  }, []);

  return <div>Seconds passed: {count}</div>;
}

I am also familiar with React Router for routing and server-side rendering (Next.js) at a basic level.