react 中文文档案例四 （登陆登出按钮）

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

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;
    
        if (isLoggedIn) {
            button = <LogoutButton onClick={this.handleLogoutClick} />;
        } else {
            button = <LoginButton onClick={this.handleLoginClick} />;
        }
  
        return (
            <div>
                <Greeting isLoggedIn={isLoggedIn} />
                {button}
            </div>
        );
    }
}
  
function UserGreeting(props) {
    return <h1>Welcome back!</h1>;
}
  
function GuestGreeting(props) {
    return <h1>Please sign up.</h1>;
}
  
function Greeting(props) {
    const isLoggedIn = props.isLoggedIn;
    if (isLoggedIn) {
      return <UserGreeting />;
    }
    return <GuestGreeting />;
}
  
function LoginButton(props) {
    return (
      <button onClick={props.onClick}>
        Login
      </button>
    );
}
  
function LogoutButton(props) {
    return (
      <button onClick={props.onClick}>
        Logout
      </button>
    );
}
  
ReactDOM.render(
    <LoginControl />,
    document.getElementById('root')
);
  

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

function WarningBanner(props) {
    if (!props.warn) {
      return null;
    }
  
    return (
        <div className="warning">
            Warning!
        </div>
    );
}
  
class Page extends React.Component {
    constructor(props) {
      super(props);
      this.state = {showWarning: true}
      this.handleToggleClick = this.handleToggleClick.bind(this);
    }
  
    handleToggleClick() {
      this.setState(prevState => ({
        showWarning: !prevState.showWarning
      }));
    }
    
    render() {
      return (
        <div>
          <WarningBanner warn={this.state.showWarning} />
          <button onClick={this.handleToggleClick}>
            {this.state.showWarning ? 'Hide' : 'Show'}
          </button>
        </div>
      );
    }
  }
  
ReactDOM.render(
    <Page />,
    document.getElementById('root')
);