Updating parent state from child components not working in reactjs

Question

I was going through react official documentation when I struck upon an example which updates the parent component through child component callbacks. I was able to understand how the flow works. However, when I tried to optimize the code further it failed to update the component via callbacks.

The Original Code:

https://codepen.io/gaearon/pen/QKzAgB?editors=0010

My code change:

    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};
    this.button = <MyButton message="Login" onClick={this.handleLoginClick} />;
  }

  handleLoginClick() {
    this.setState({isLoggedIn: true});
  }

  handleLogoutClick() {
    this.setState({isLoggedIn: false});
  }

  render() {
    const isLoggedIn = this.state.isLoggedIn;
    if (isLoggedIn) {
      this.button = <MyButton message="Logout" onClick={this.handleLogoutClick} />;
    } else {
      this.button = <MyButton message="Login" onClick={this.handleLoginClick} />;
    }

    return (
      <div>
        <Greeting isLoggedIn={isLoggedIn} />
        {this.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 />;
}

class MyButton extends React.Component {
  constructor(props) {
    super(props);
    this.message=props.message;
    this.click=props.onClick;
  }
  render() {
    return (
    <button onClick={this.click}> 
        {this.message}
    </button>  
    );
  }
}

ReactDOM.render(
  <LoginControl />,
  document.getElementById('root')
);

Answer 1

Ok the main problem here is that you are trying to assign to many things to "this". React does not track changes and re-renders when component's method or properties changes. try to avoid this pattern and use state and props directly. Only changes to state or props will cause a component to re-render. In you situation you can look at this code:

   class LoginControl extends React.Component {


     state = {isLoggedIn : false}

  handleLoginClick = () => {
    this.setState({isLoggedIn: true});
  }

  handleLogoutClick = () => {
    this.setState({isLoggedIn: false});
  }

  button = () => {

    const message = this.state.isLoggedIn ? "Logout" : "Login";
    const onClick = this.state.isLoggedIn ? this.handleLogoutClick : this.handleLoginClick;
    return <MyButton message={message} onClick={onClick} />
  }

  render() {


    return (
      <div>
        <Greeting isLoggedIn={this.state.isLoggedIn} />
       {this.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 />;
}

class MyButton extends React.Component {
  constructor(props) {
    super(props);
    this.message=props.message;
    this.click=props.onClick;
  }
  render() {
    return (
    <button onClick={this.props.onClick}> 
        {this.props.message}
    </button>  
    );
  }
}

ReactDOM.render(
  <LoginControl />,
  document.getElementById('root')
);