How can I use useState in class components?

Can you explain how to use useState in class components?

Actually, useState is a Hook that can only be used in functional components. In class components, you manage state using this.state and this.setState.

So, how do I manage state in a class component then?

In class components, you initialize state in the constructor and update it using this.setState. For example, you can do this:

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return <button onClick={this.increment}>{this.state.count}</button>;
  }
}

What if I want to use both class and functional components in my app?

You can definitely mix class and functional components in your app! Just remember to use useState in functional components and this.state in class components.