// Child component
class Child extends React.Component {
  // First thing called when component loaded
  constructor(props) {
    console.log("constructor");
    super(props);
    this.state = {
      value: this.props.value,
      color: "green"
    };
  }

  // static method
  // dont have access of 'this'
  // return object will update the state
  static getDerivedStateFromProps(props, state) {
    console.log("getDerivedStateFromProps");
    return {
      value: props.value,
      color: props.value % 2 === 0 ? "green" : "red"
    };
  }

  // skip render if return false
  shouldComponentUpdate(nextProps, nextState) {
    console.log("shouldComponentUpdate");
    // return nextState.color !== this.state.color;
    return true;
  }

  // In between before real DOM updates (pre-commit)
  // has access of 'this'
  // return object will be captured in componentDidUpdate
  getSnapshotBeforeUpdate(prevProps, prevState) {
    console.log("getSnapshotBeforeUpdate");
    return { oldValue: prevState.value };
  }

  // Calls after component updated
  // has access of previous state and props with snapshot
  // Can call methods here
  // setState inside this will cause infinite loop
  componentDidUpdate(prevProps, prevState, snapshot) {
    console.log("componentDidUpdate: ", prevProps, prevState, snapshot);
  }

  static getDerivedStateFromError(error) {
    console.log("getDerivedStateFromError");
    return { hasError: true };
  }

  componentDidCatch(error, info) {
    console.log("componentDidCatch: ", error, info);
  }

  // After component mount
  // Good place to start AJAX call and initial state
  componentDidMount() {
    console.log("componentDidMount");
    this.makeAjaxCall();
  }

  makeAjaxCall() {
    console.log("makeAjaxCall");
  }

  onClick() {
    console.log("state: ", this.state);
  }

  render() {
    return (
      <div style={{ border: "1px solid red", padding: "0px 10px 10px 10px" }}>
        <p style={{ color: this.state.color }}>Color: {this.state.color}</p>
        <button onClick={() => this.onClick()}>{this.props.value}</button>
      </div>
    );
  }
}

// Parent component
class Parent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: 1 };

    this.tick = () => {
      this.setState({
        date: new Date(),
        value: this.state.value + 1
      });
    };
  }

  componentDidMount() {
    setTimeout(this.tick, 2000);
  }

  render() {
    return (
      <div style={{ border: "1px solid blue", padding: "0px 10px 10px 10px" }}>
        <p>Parent</p>
        <Child value={this.state.value} />
      </div>
    );
  }
}

function App() {
  return (
    <React.Fragment>
      <Parent />
    </React.Fragment>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>