reactjs - React multiple contexts

Question

I am using functions which are passed down through context.

ChildComponent.contextType = SomeContext;

Now I use this.context.someFunction();. This works.

How can I do this if I need functions from two different parent components?

Answer 1

You can still use function-as-a-child consumer nodes with the 16.3 Context API, which is what the React documentation suggests doing:

// Theme context, default to light theme
const ThemeContext = React.createContext('light');

// Signed-in user context
const UserContext = React.createContext({
  name: 'Guest',
});

class App extends React.Component {
  render() {
    const {signedInUser, theme} = this.props;

    // App component that provides initial context values
    return (
      <ThemeContext.Provider value={theme}>
        <UserContext.Provider value={signedInUser}>
          <Layout />
        </UserContext.Provider>
      </ThemeContext.Provider>
    );
  }
}

function Layout() {
  return (
    <div>
      <Sidebar />
      <Content />
    </div>
  );
}

// A component may consume multiple contexts
function Content() {
  return (
    <ThemeContext.Consumer>
      {theme => (
        <UserContext.Consumer>
          {user => (
            <ProfilePage user={user} theme={theme} />
          )}
        </UserContext.Consumer>
      )}
    </ThemeContext.Consumer>
  );
}

To use functions in context in your component you'd typically wrap your component in a HOC so the context is passed in as props:

export const withThemeContext = Component => (
  props => (
    <ThemeContext.Consumer>
      {context => <Component themeContext={context} {...props} />}
    </ThemeContext.Consumer>
  )
)

const YourComponent = ({ themeContext, ...props }) => {
  themeContext.someFunction()
  return (<div>Hi Mom!</div>)
}

export default withThemeContext(YourComponent)

If you're running React 16.8+ you can also use hooks to do this more cleanly without using HOCs:

import React, { useContext } from "react"

const YourComponent = props => {
  const theme = useContext(ThemeContext)
  const user = useContext(UserContext)
}

Or, if you consume these contexts a lot, you can even make a custom hook to simplify further:

const useTheme = () => useContext(ThemeContext)
const useUser = () => useContext(UserContext)

const YourComponent = props => {
  const theme = useTheme()
  const user = useUser()
}