Share global data without passing through props, does make components less reusable
this.context will return the nearest ancestor's value of that context type, so can specialize further down tree
For multiple contexts, just add multiple providers and contexts if needed
Usage
1) Create context(seperate file? theme-context.js)
PizzaContext.js
import React from "react";
const ThemeContext = React.createContext('light'); //default value
export default ThemeContext;
2) Add Provider
function App(){
return (
<ThemeContext.Provider value="dark"> //overrides default
<Toolbar />
</ThemeContext.Provider>
);
}
3) Now anything in subtree of Provider can access data
useContext hook can access data
import ThemeContext from "./ThemeContext";
export default function Pizza(props) {
const theme = useContext( ThemeContext );
return <div>{theme}</div>;
}
Contexttypes can access data in classes
import ThemeContext from "./ThemeContext";
class ThemedButton extends React.Component {
static contextType = ThemeContext;
render() {
return <Button theme={this.context} />;
}
}
Advanced
Updating Context and Consumers Example
Pass a ft with the context that lets you toggle it
theme-context.js
export const themes = {
light: { foreground: '#000000 },
dark: {foreground: '#ffffff' },
};
//default should match type of expected
export const ThemeContext = React.createContext({
theme: themes.dark,
toggleTheme: () => {},
});
theme-toggler-button.js
import {ThemeContext} from './theme-context';
function ThemeTogglerButton() {
return (
<ThemeContext.Consumer>
{({theme, toggleTheme}) => (
<button
onClick={toggleTheme}
style={{backgroundColor: theme.background}}>
Toggle Theme
</button>
)}
</ThemeContext.Consumer>
);
}
export default ThemeTogglerButton;
app.js
import {ThemeContext, themes} from './theme-context';
import ThemeTogglerButton from './theme-toggler-button';
class App extends React.Component {
constructor(props) {
super(props);
this.toggleTheme = () => {
this.setState(state => ({
theme:
state.theme === themes.dark
? themes.light
: themes.dark,
}));
};
this.state = {
theme: themes.light,
toggleTheme: this.toggleTheme,
};
}
render() {
return (
<ThemeContext.Provider value={this.state}>
<Content />
</ThemeContext.Provider>
);
}
}
//some intermidate components
function Content() {
return (
<div>
<ThemeTogglerButton />
</div>
);
}
ReactDOM.render(<App />, document.root);