React 16.3 context example in ~30 lines of code.

App.jsx

import * as React from 'react';
import SomeContext from './SomeContext.jsx';

const App = () => (
  <SomeContext.Provider value={{ foo: 'bar' }}>
    <App />
  </SomeContext.Provider>
);

export default App;

SomeContext.jsx

import * as React from 'react';

export const Context = React.createContext();

export default {
	Provider: Context.Provider,
	Consumer: Context.Consumer,
};

SomewhereDownApp.jsx

import * as React from 'react';
import SomeContext from './SomeContext.jsx';

// My parent (or grandparent, or great grandparent, etc) is App (which has Context.Provider).
const SomewhereDownApp = () => (
  <div>
    <SomeContext.Consumer>
      {context => (
        <p>Foo: {context.foo}</p>
      )}
    </SomeContext.Consumer>
  </div>
);

export default SomewhereDownApp;