react-context-decorator-1.js

const ColorContext = React.createContext();

class App extends React.Component {
  constructor(props) {
    super(props);

    this.updateColor = (newColor) => this.setState({ color: newColor })

    this.state = {
      color: 'red',
      updateColor: this.updateColor,
    };
  }
  render() {
    return (
      <ColorContext.Provider value={this.state}>
        <Button />
      </ColorContext>
    );
  }
}

class Button extends React.Component {
  render() {
    return (
      <ColorContext.Consumer>
        {(context) => 
          <button
            style={{ color: context.color }}
            onClick={() => context.updateColor('green')}>
            Click Me!
          </button>
        }
      </Consumer>
    );
  }
}

// ...