const Context = createReactContext(defaultValue);
/*
	<Context.Provider value={providedValue}>
		{children}
	</Context.Provider>

	...

	<Context.Consumer>
		{value => children}
	</Context.Consumer>
*/

// @flow
import React, { type Node } from 'react';
import createReactContext, { type Context } from 'mini-create-react-context';

type Theme = 'light' | 'dark';
// Pass a default theme to ensure type correctness
const ThemeContext: Context<Theme> = createReactContext('light');

class ThemeToggler extends React.Component<
  { children: Node },
  { theme: Theme }
> {
  state = { theme: 'light' };
  render() {
    return (
      // Pass the current context value to the Provider's `value` prop.
      // Changes are detected using strict comparison (Object.is)
      <ThemeContext.Provider value={this.state.theme}>
        <button
          onClick={() => {
            this.setState(state => ({
              theme: state.theme === 'light' ? 'dark' : 'light'
            }));
          }}
        >
          Toggle theme
        </button>
        {this.props.children}
      </ThemeContext.Provider>
    );
  }
}

class Title extends React.Component<{ children: Node }> {
  render() {
    return (
      // The Consumer uses a render prop API. Avoids conflicts in the
      // props namespace.
      <ThemeContext.Consumer>
        {theme => (
          <h1 style={{ color: theme === 'light' ? '#000' : '#fff' }}>
            {this.props.children}
          </h1>
        )}
      </ThemeContext.Consumer>
    );
  }
}

<Context.Provider>
  <div/>
  <div/>
</Context.Provider>

<Context.Provider>
  <div>
    <div/>
    <div/>
  </div>
</Context.Provider>