react hooks state placement code example

Example 1: update state in useState hook

// declare state using useState hook.
// someState is set to someInitialState
const [someState, setSomeState] = useState(someInitialState);

// setSomeState updates the current state 
setSomeState(someOtherState);

Example 2: equivalent class, hooks and function components

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

  render() {
    return (
      <div>
        <p>You clicked {this.state.count} times</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
          Click me
        </button>
      </div>
    );
  }
}