React Hooks Tutorial - 8 - Memo and PureComponent

In react, components can be defined as functions or ES6 classes. All class components are sub classes of either Component or PureComponent. To understand when PureComponent base class is used for declaring your class component, it is important to understand when a react component defined as a sub class of Component re-renders.

When a class component is a sub class of Component, it is re-rendered whenever:
1) state changes
2) context changes
3) parent re-renders
4) props change
You can see from the above that a component is re-rendered whenever its parent re-renders though its context, state or props haven't changed. To prevent a component from re-rendering because of its parent's re-render, you can declare it as a sub class of PureComponent. PureComponent implements shouldComponentUpdate out of the box. It does a shallow comparison of props and state. If the state and props haven't changed, react doesn't re-render the component even if the parent re-renders. Since this is a shallow comparison, pureComponent should be avoided if your component is deeply nested because react can produce false-negatives for deeper differences. It should only be used if the component is pure.

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[renatodati]

Thank you so much for the class. It helped me a lot