React multiple contexts
Another solution is to create a separate context providing the other contexts:
import React, { createContext, memo, useContext } from "react";
import isEqual from "react-fast-compare";
export const MultiContext = createContext(null);
MultiContext.displayName = "MultiContext";
export const MultiContextProvider = memo(
function({ map, children }) {
const contextMap = {};
for (const i in map) {
contextMap[i] = useContext(map[i]);
}
return (
<MultiContext.Provider value={contextMap}>
{children}
</MultiContext.Provider>
);
},
(prevProps, nextProps) => isEqual(prevProps.children, nextProps.children)
);
MultiContextProvider.displayName = "MultiContextProvider";
Example usage:
class DemoConsumer extends React.Component {
static contextType = MultiContext;
render() {
return JSON.stringify({
someValue: this.context.SomeContext.someValue,
otherValue: this.context.OtherContext.otherValue,
});
}
}
function App() {
return (
<MultiContextProvider map={{ SomeContext, OtherContext }}>
<MultiContextDemoClassConsumer />
</MultiContextProvider>
);
}
Demo:
const {
createContext,
memo,
useContext,
useState,
useEffect,
} = React;
const MultiContext = createContext(null);
MultiContext.displayName = "MultiContext";
const MultiContextProvider = memo(
function({ map, children }) {
console.log("render provider");
const contextMap = {};
for (const i in map) {
contextMap[i] = useContext(map[i]);
}
return (
<MultiContext.Provider value={contextMap}>
{children}
</MultiContext.Provider>
);
},
(prevProps, nextProps) => isEqual(prevProps.children, nextProps.children)
);
MultiContextProvider.displayName = "MultiContextProvider";
const initialMinutes = new Date().getMinutes();
const MinutesContext = createContext(initialMinutes);
MinutesContext.displayName = "MinutesContext";
const IncrementContext = createContext(0);
IncrementContext.displayName = "IncrementContext";
class MultiContextDemoClassConsumer extends React.Component {
static contextType = MultiContext;
render() {
return JSON.stringify(this.context);
}
}
const multiContextMap = { MinutesContext, IncrementContext };
function App() {
const forceUpdate = useForceUpdate();
const [minutes, setMinutes] = useState(initialMinutes);
useEffect(() => {
const timeoutId = setInterval(() => {
// console.log('set minutes')
setMinutes(new Date().getMinutes());
}, 1000);
return () => {
clearInterval(timeoutId);
};
}, [setMinutes]);
const [increment, setIncrement] = useState(0);
console.log("render app");
return (
<MinutesContext.Provider value={minutes}>
<IncrementContext.Provider value={increment}>
<MultiContextProvider map={multiContextMap}>
<MultiContextDemoClassConsumer />
</MultiContextProvider>
<button onClick={() => setIncrement(i => i + 1)}>Increment</button>
<button onClick={forceUpdate}>Force Update</button>
</IncrementContext.Provider>
</MinutesContext.Provider>
);
}
ReactDOM.render(<App />, document.getElementById("root"));
<script type="module">
import React from 'https://dev.jspm.io/react@16';
import ReactDOM from 'https://dev.jspm.io/react-dom@16';
import useForceUpdate from 'https://dev.jspm.io/[email protected]';
import isEqual from 'https://dev.jspm.io/[email protected]';
window.React = React;
window.ReactDOM = ReactDOM;
window.useForceUpdate = useForceUpdate.default;
window.isEqual = isEqual;
</script>
<div id="root"></div>
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()
}
You could also simply merge all your contexts into a single one:
const AppContext = React.createContext({
user: { name: 'Guest' },
theme: 'light',
})
ChildComponent.contextType = AppContext;
Done. You simply need to merge the new values if you have a different context in some parts of you app (like a different theme or user).