add and remove class in html with react hooks code example

Example 1: setting className using useEffect

useEffect(() => {
  document.body.className = 'signin';
  return () => { document.body.className = ''; }
});

Example 2: react hooks

import React, { useState } from 'react';

function Example() {
  // Declare a new state variable, which we'll call "count"  const [count, setCount] = useState(0);
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}