Are updated to the context not propagated via the ususal rerenders? As I cannot see my logs / color changes when context changes.
The updates to context values doesn’t trigger re-render for all the children of the provider, rather only components that are rendered from within the Consumer, so in your case although number component contains the Consumer, Number component isn’t re-rendered, rather just the render function within the Consumer and hence the value changes on context updates. This way it is quite a lot performant as it doesn’t trigger re-renders for all of its children.
Are all the consumers to that Provider updated or not ?
All consumers to that Provider will go through an update cycle but whether or not they re-render is decided by the react virtual DOM comparison. A demo of this you can see in the console for this sandbox
EDIT
What you need to make sure is that the components are rendered as children of the ContextProvider component and you are passing handlers to it instead of rendering them inline and updating the state of ContextProvider because that will trigger a re-render of all components that are within the ContextProvider
Performant usage
App.js
constructor() {
super();
this.state = {
number: Math.random() * 100,
text: "testing context api"
updateNumber: this.updateNumber,
};
}
render() {
return (
<AppContext.Provider
value={this.state}
>
{this.props.children}
</AppContext.Provider>
);
}
index.js
class Data extends React.Component {
render() {
return (
<div>
<h1>Welcome to React</h1>
<Number />
<Text />
<TestComp />
<AppContext.Consumer>
{({ updateNumber }) => (
<button onClick={updateNumber}>Change Number </button>
)}
</AppContext.Consumer>
</div>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(
<App>
<Data />
</App>,
rootElement
);
Less Performant usage
App.js
class App extends Component {
constructor() {
super();
this.state = {
number: Math.random() * 100,
text: "testing context api"
};
}
updateNumber = () => {
const randomNumber = Math.random() * 100;
this.setState({ number: randomNumber });
};
render() {
return (
<AppContext.Provider value={this.state}>
<div>
<h1>Welcome to React</h1>
<Number />
<Text />
<TestComp />
<button onClick={this.updateNumber}>Change Number </button>
</div>
</AppContext.Provider>
);
}
}