[React Fundamentals] Component Lifecycle

React components have a lifecycle, and you are able to access specific phases of that lifecycle. This lesson will introduce mounting and unmounting of your React components.

import React from 'react';
import ReactDOM from 'react-dom';

export default class App extends React.Component {
    constructor(){
        super();
        this.state = {
            val: 0
        }
    }
    update(){
        this.setState({
            val: this.state.val + 1
        })
    }
    componentWillMount(){
        console.log("Component Will Mount");
    }
    render() {
        console.log("rendering");
        return (
            <div>
                <button onClick={this.update.bind(this)}>{this.state.val}</button>
            </div>
        )
    }
    componentDidMount(){
        console.log("Component Did Mount");
    }
}

"componentWillMount" happen before rendering, "state" and "props" are ready, but DOM is not rendered yet.

"componentDidMount" happen after component rendered to the DOM, can access DOM Node.