ShouldComponentUpdate

shouldComponentUpdate(nextProps, nextState) is a lifecycle method in React class components. It is called before rendering when a component receives new props or state. The method receives the next props and next state and should return a boolean that indicates whether React should proceed with rendering.

If it returns true (the default), the update continues and render is called. If false, React skips rendering for that update, and the DOM is not updated for this cycle. This method is a common target for performance optimizations, allowing developers to prevent unnecessary renders when inputs have not meaningfully changed.

Implementations typically compare relevant fields using a shallow equality check and avoid mutating props or state. Because a shallow comparison may miss deeper changes, care is needed to identify which data actually influences rendering. ShouldComponentUpdate should be pure and free of side effects; avoid calling setState or causing I/O inside this method.

Alternatives and related approaches include using React.PureComponent, which implements a shallow prop/state comparison by default, and functional components with React.memo (or useMemo/useCallback in combination with hooks). These patterns offer built-in optimizations without manually writing shouldComponentUpdate.

Notes: shouldComponentUpdate is not called on the initial render. In modern React patterns, developers often prefer PureComponent or memoized functional components to achieve similar optimization goals with less boilerplate, reserving shouldComponentUpdate for bespoke or highly specialized performance tuning.