create-react-context
Polyfill for the proposed React context API
Install
yarn add create-react-context
You'll need to also have react and prop-types installed.
API
const Context = createReactContext(defaultValue);
// <Context.Provider value={providedValue}>{children}</Context.Provider>
// ...
// <Context.Consumer>{value => children}</Context.Consumer>
Example
// @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>
);
}
}
Compatibility
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>