create-react-context

What is create-react-context?

The create-react-context package is a polyfill for the React context API for React versions below 16.3. It allows you to create a context object which can be used to pass data through the component tree without having to pass props down manually at every level.

What are create-react-context's main functionalities?

Creating Context

This feature allows you to create a new context object. You can set a default value that can be used when a component does not have a matching Provider above it in the tree.

{"const MyContext = createReactContext(defaultValue);"}

Provider Component

The Provider component is used to set the value of the context to be accessible by all components that are its descendants.

{"<MyContext.Provider value={/* some value */}>{/* some child components */}</MyContext.Provider>"}

Consumer Component

The Consumer component is used to read the current context value, provided by the nearest matching Provider above it in the tree.

{"<MyContext.Consumer>{value => /* render something based on the context value */}</MyContext.Consumer>"}

Other packages similar to create-react-context

react-redux

React Redux uses a similar pattern with a Provider and connect function to pass down state from a Redux store. It's more complex and tailored for state management with Redux.

mobx-react

MobX-react provides components like Provider and inject to connect React components to MobX stores. It's similar but is specifically designed to work with MobX state management.

react-broadcast

React Broadcast is another library that provides a similar API for creating a broadcast channel that allows you to pass data through the component tree. It's less commonly used since the introduction of the official context API in React.

README

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>