React条件渲染

class LoginControl extends React.Component {
  constructor(props) {
    super(props);
    this.handleLoginClick = this.handleLoginClick.bind(this);
    this.handleLogoutClick = this.handleLogoutClick.bind(this);
    this.state = {isLoggedIn: false};
  }
 
  handleLoginClick() {
    this.setState({isLoggedIn: true});
  }
 
  handleLogoutClick() {
    this.setState({isLoggedIn: false});
  }
 
  render() {
    const isLoggedIn = this.state.isLoggedIn;
 
    let button = null;
    if (isLoggedIn) {
      button = <LogoutButton onClick={this.handleLogoutClick} />;
    } else {
      button = <LoginButton onClick={this.handleLoginClick} />;
    }
 
    return (
      <div>
        <Greeting isLoggedIn={isLoggedIn} />
        {button}
      </div>
    );
  }
}
 
ReactDOM.render(
  <LoginControl />,
  document.getElementById(‘example‘)
);