The React.memo() function is the modern equivalent of the PureComponent class. Memoized components avoid re-rendering if the component data hasn't changed. In the past, you would extend your class component with PureComponent. This would automatically handle checking whether the component data has changed or not and whether or not the component should re-render.
The challenge with this approach is that it is now common for large React applications to have a lot of functional components. Before React.memo(), there was no way to memorize components so that they could avoid re-rendering if no data changes happened. Now, you can pass your functional components to React.memo() and they'll behave like PureComponent.
You can read more about React.memo() here: https://reactjs.org/docs/react-api.html#reactmemo.
