App.js

class App extends React.Component {
  state = {
    counter: 0,
  }

  componentDidMount() {
    // if used in here, that's works well without need to pass a CB in the second argument of setState
    // that's because the setState in this context is synchronous

    // setInterval(() => {
    //   this.increment();
    // }, 3000)
  }

  componentDidUpdate() {
    console.log('updated', this.state);
  }

  logMe = () => {
    console.log(this.state.counter);
  }

  increment = () => {
    // works in both scenarios
    this.setState(state => ({ counter: state.counter + 1 }));
    this.setState(state => ({ counter: state.counter + 1 }), this.logMe); // use a callback to get state just when is updated
  }

  incrementOutDated = () => {
    // When is trigged for a non-behavior of the user, the setState is executed synchronous
    this.setState(state => ({ counter: state.counter + 1 }));
    this.setState(state => ({ counter: state.counter + 1 }));

    console.log(this.state.counter);
  }

  render() {
    return (
      <div className="App">
        {/* using this.increase works well */ }
        {/* When the action come from a behavior of the user, the setState is executed asynchronous */ }
        <button onClick={this.incrementOutDated}>Add 1 more</button>
          <h3>{this.state.counter}</h3>
      </div>
    );
  }
}