A Higher Order Component (HOC) is a function in React that takes a component as input and returns a new component with enhanced props or behavior. HOCs are often used to share common functionality across multiple components, making code reuse and abstraction easier in React applications.

When a component extends React.PureComponent, it automatically implements shouldComponentUpdate with a shallow comparison of state and props. This shallow comparison helps in optimizing rendering by preventing unnecessary updates when there are no actual changes to state or props.

To render tooltips directly under the body tag and ensure they appear on top, you can use ReactDOM.createPortal(). This function allows you to render a React component at a different DOM location, ensuring it's not affected by the hierarchy of nested components. This is commonly used to create overlays like tooltips and modals.

In React Router, the "render" prop in the Route component allows passing props directly to the rendered component. This is particularly useful when you need to pass additional props or perform logic before rendering the component associated with a specific route. The other options ("component," "children," and "props") are not used for this specific purpose.

In a large application with complex state changes, the library that can help manage state updates using a more concise and readable syntax while ensuring immutability is Immer. Immer simplifies state updates by allowing you to write code that appears mutable but actually produces immutable updates. It's particularly useful when dealing with deeply nested state structures.

The useReducer hook in React is particularly useful when the next state depends on the global state, often referred to as the previous state. It allows developers to manage state transitions and complex logic more effectively, making it a valuable tool in scenarios where state updates are interdependent.

The getStaticProps function in Next.js is used to fetch data at build time. It allows you to pre-render pages with data before they are served to the client. This approach improves performance as the data is fetched and generated during the build process, reducing the need for runtime data fetching. It's a key feature for static site generation (SSG) in Next.js.

Memoization is an immutable state handling technique that can help mitigate unnecessary component re-renders. It involves caching the results of expensive function calls based on their input parameters. When the same input parameters are encountered again, the cached result is returned, reducing the need for re-computation and re-rendering.

In React Native, for platform-specific code, you can use filename extensions like .ios.js for iOS-specific code and .android.js for Android-specific code. These filename extensions allow you to write platform-specific logic in separate files, making it easier to maintain and customize your app's behavior for different platforms. .platform.js, .native.js, and .react.js are not standard extensions for platform-specific code in React Native.

The process by which a service worker takes control of a page and becomes active is known as activation. Service workers go through several lifecycle phases, and activation is the point at which the service worker becomes active and can start intercepting network requests.