How are custom methods called in React components?

Question

JavaScript

There is the following code, there is a component in which there are two methods componentDidMount, componentWillUnmount, one cyclically updates the state, the other stops updating how they work if they are not explicitly called. Code - creates the time, and constantly updates the state of the time.

class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  componentDidMount() {
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>It is {this.state.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}

ReactDOM.render(
  <Clock />,
  document.getElementById('root')
);

Answer 1

tick is called every second, and in its body there is setState, which, after it has finished, automatically calls the render () method. So every second your component is rerendered