From the React website: "When a component's props or state change, React decides whether an actual DOM update is necessary by comparing the newly returned elem

From the React website: "When a component's props or state change, React decides whether an actual DOM update is necessary by comparing the newly returned element with the previously rendered one." My point is that if a component doesn't receive a setState or new props it just doesn't start the rendering cycle at all (AFAIK), so shouldComponentUpdate doesn't get called at all.