ReactPureComponent

React.PureComponent is a base class in the React library that extends React.Component and provides a built-in optimization for rendering. It implements a default shouldComponentUpdate method that performs a shallow comparison of the current props and state with the next props and state. If the shallow comparison reports no changes, React skips re-rendering the component and its subtree, which can reduce unnecessary updates.

Usage typically involves extending PureComponent rather than Component, for example class MyComponent extends React.PureComponent. The canonical name is React.PureComponent; some discussions may refer to it informally as ReactPureComponent.

How it works and when to use it: PureComponent relies on shallow equality for props and state. Primitive values are compared by value, while objects and arrays are compared by reference. This makes PureComponent effective when your data is treated as immutable or when you replace objects and arrays rather than mutating them in place. It can improve performance for frequently rendered components whose props/state do not change often.

Caveats: Since the check is shallow, deep mutations may not trigger a re-render. Mutating nested data without changing references can lead to stale output. If your component depends on deep changes or complex equality logic, you may need to implement shouldComponentUpdate yourself or use other optimization strategies.

Relation to other patterns: For functional components, a similar effect is achieved with React.memo. PureComponent is a class-based alternative that complements immutable data patterns and can simplify performance tuning in class components.