Polyfill for the proposed React context API
yarn add create-react-contextYou'll need to also have react and prop-types installed.
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 '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> ); } }This package only "ponyfills" the React.createContext API, not other unrelated React 16+ APIs. If you are using a version of React <16, keep in mind that you can only use features available in that version.
For example, you cannot pass children types aren't valid pre React 16:
<Context.Provider> <div/> <div/> </Context.Provider>It will throw A valid React element (or null) must be returned. You may have returned undefined, an array or some other invalid object. because <Context.Provider> can only receive a single child element. To fix the error just wrap everyting in a single <div>:
<Context.Provider> <div> <div/> <div/> </div> </Context.Provider>