react before component mount code example

Example 1: react lifecycle example

class Test extends React.Component {
  constructor() {
    console.log('Constructor')
    super();
    this.state = {
      count: 0
    };
  }

  componentDidMount() {
    console.log("component did mount");
  }
  componentDidUpdate() {
    console.log("component did update");
  }

  onClick = () => {
    this.setState({ count: this.state.count + 1 });
  };
  render() {
    console.log("render");
    return (
      <div>
        Hello Test
        <button onClick={this.onClick}>
      		{this.state.count}
		</button>
      </div>
    );
  }
}


//--for first time
//Constructor
//render
//component did mount
//--for any update
//render
//component did update

Example 2: lifecycles if reactjs

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

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

Example 3: shouldcomponentupdate

shouldComponentUpdate(nextProps, nextState) {
  return true;
}

Example 4: component did mmount

componentDidUpdate(prevProps, prevState, snapshot)