React/State.html at master · Saseungwon/React · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Example</title>
</head>
<body>

  <div id="root"></div>
  <script crossorigin src="https://unpkg.com/react@17/umd/react.development.js"></script>
  <script crossorigin src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
  <script type="text/javascript">
    console.log(React);
    console.log(ReactDOM)


    class Component extends React.Component {
      // state는 객체 형태로만 제공됨
      state = {
        count: 0,
      };

      render(){
        return(
          <div>
             <h1>{this.props.message} 이것은 class로 만든 컴포넌트 입니다.</h1>
             <p>{this.state.count}</p>
          </div>
        );
      }

      componentDidMount(){
        setTimeout(() => {
          // this.state.count = this.state.count + 1;   => 이런식으로 하면 state 안에 접근불가
          this.setState({count: this.state.count + 1}); // setState 사용해야함
        }, 1000);
      }

      static defaultProps = {
        message: "기본값2"
      };
    }

    ReactDOM.render(
      <Component message="기본값 아님"/>,
      document.querySelector("#root")
    );
  </script>

</body>
</html>