React.js

Functional components

function Welcome(props) {
  return <h1>Hello, {this.props.name}</h1>;
}

Class components

class Welcome extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}

Class components

The only method you must define in a React.Component subclass is called render(). All the other methods are optional.

Class components

class Header extends React.Component {
  constructor(props) {
    super(props);
    // this.state = {favoritecolor: "red"};
  }
  static getDerivedStateFromProps(props, state) {
    // return {favoritecolor: props.favcol };
  }
  componentDidMount() {
    // this.setState({favoritecolor: "yellow"})
  }
  shouldComponentUpdate(nextProps, nextState) {
    // return nextState.favoritecolor !== this.state.favoritecolor;
  }
  getSnapshotBeforeUpdate(prevProps, prevState) {
    //
  }
  componentDidUpdate(prevProps, prevState, snapshot) {
    // if (this.props.userID !== prevProps.userID) {
    //   this.fetchData(this.props.userID);
    // }
  }
  componentWillUnmount() {
    // alert("The component named Header is about to be unmounted.");
  }
  render() {
    return (
      <h1>My Favorite Color is {this.state.favoritecolor}</h1>
    );
  }
}

Component lifecycle

Mount phase:

• constructor()
• static getDerivedStateFromProps()
• render()
• componentDidMount()

Component lifecycle

Update phase:

• static getDerivedStateFromProps()
• shouldComponentUpdate()
• render()
• getSnapshotBeforeUpdate()
• componentDidUpdate()

Component lifecycle

Unmount phase:

• componentWillUnmount()

Component lifecycle

Error handling

• static getDerivedStateFromError()
• componentDidCatch()

Resources

• https://reactjs.org/docs/react-component.html#the-component-lifecycle
• https://projects.wojtekmaj.pl/react-lifecycle-methods-diagram/
• https://wavez.github.io/react-hooks-lifecycle/