react-af

TL;DR

• Allows you to code using certain React.next features today!
• Perfect for component library maintainers.
• It does for React what Babel does for JavaScript.
• Support getDerivedStateFromProps on older versions of React.
• Supports Fragment on older versions of React.
• Supports createContext (the new context API) on older versions of React.

What is this project?

Starting with React 17, several class component lifecycles will be deprecated: componentWillMount, componentWillReceiveProps, and componentWillUpdate (see React RFC 6).

One problem that React component library developers face is that they don't control the version of React that they run on — this is controlled by the consuming application. This leaves library developers in a bit of a quandary. Should they use feature detection or code to the lowest denominator?

react-af emulates newer features of React on older versions, allowing developers to concentrate on the business problem and not the environment.

Install

Install react-af using npm:

$ npm install react-af --save

or with Yarn:

$ yarn add react-af

Import

In your code, all you need to do is change the React import from this:

import React from 'react';

To this:

import React from 'react-af';

That's it! You can now code your library components as though they are running on a modern React (not all features supported... yet), even though your code may be running on an older version.

react-af imports from react under the hood (it has a peerDependency of React >=15), patching or passing through features where necessary.

API

Here are the modern React features that you can use, even if yur code is running on older version of React 15 or React 16.

getDerivedStateFromProps

react-af supports new static lifecycle getDerivedStateFromProps.

Here is an example component written using componentWillReceiveProps.

class ExampleComponent extends React.Component {
  state = { text: this.props.text };

  componentWillReceiveProps(nextProps) {
    if (this.props.text !== nextProps.text) {
      this.setState({
        text: nextProps.text
      });
    }
  }
}

And here it is after converting to be compatible with modern React.

class ExampleComponent extends React.Component {
  state = {};

  static getDerivedStateFromProps(nextProps, prevState) {
    return prevState.text !== nextProps.text
      ? {
        text: nextProps.text
      }
      : null;
  }
}

Fragment

Starting with React 16.2, there is a new <Fragment /> component that allows you to return multiple children. Prior to 16.2, you needed to wrap multiple children in a wrapping div.

With react-af, you can use React.Fragment on older versions of React as well.

import React, { Fragment } from 'react-af';

const Weather = ({ city, degrees }) => (
  <Fragment>
    <div>{city}</div>
    <div>{degrees}℉</div>
  </Fragment>
);

The code above works natively in React 16.2 and greater. In lesser versions of React, Fragment is replaced with a div automatically.

createContext

React 16.3 also added support for the new context API. Well react-af supports that as well.

Here's an example take from Kent Dodds's article React’s new Context API.

import React, { createContext, Component } from 'react-af';

const ThemeContext = createContext('light')
class ThemeProvider extends Component {
  state = {theme: 'light'}
  render() {
    return (
      <ThemeContext.Provider value={this.state.theme}>
        {this.props.children}
      </ThemeContext.Provider>
    )
  }
}
class App extends Component {
  render() {
    return (
      <ThemeProvider>
        <ThemeContext.Consumer>
          {val => <div>{val}</div>}
        </ThemeContext.Consumer>
      </ThemeProvider>
    )
  }
}

Other projects

react-lifecycles-compat

You might also want to take a look at react-lifecycles-compat by the React team. It doesn't support Fragment or createContext and it requires additional plumbing to setup, but it's lighter and may be adequate for some projets.

create-react-context

If all you need is context support, consider using create-react-context, which is what this package uses to emulate createContext().

What's with the name?

ReactAF stands for React Always Fresh (or React As F&#%!). Your choice.