In MobX, you can track changes to your state using "Observables." Observables are the fundamental building blocks that enable you to automatically detect and track changes in your application state. Actions are used to modify state, decorators are used for defining computed properties, and Promises are typically used for handling asynchronous operations but do not directly track state changes.

When adding a new item to a list in React, it's essential to provide unique keys to each list item using the "key" prop. If unique keys are missing or incorrectly assigned, React cannot efficiently identify which items have changed, and it may re-render the entire list. Using React.memo() can help optimize functional components, but it's unrelated to this specific issue. React fragments and shouldComponentUpdate() do not directly address the key issue.

The shouldComponentUpdate method in React allows developers to manually determine whether a component should re-render in response to changes in props or state. This method returns a Boolean value - true if the component should re-render and false if it should not. It's a critical method for optimizing React components to avoid unnecessary rendering.

JSX (JavaScript XML) gets compiled into JavaScript by tools like Babel. It's important to understand that JSX is a syntax extension for JavaScript, allowing developers to write HTML-like code within their JavaScript files. This JSX code is then transformed into standard JavaScript code that browsers can understand.

The strategy that prioritizes network requests over cache but falls back to cache if the network is unavailable is called "Cache-First." This approach optimizes performance by serving cached content when possible while ensuring the latest data is fetched when the network is available, making it a common strategy for progressive web applications (PWAs) and service workers.

When you have pages that need to be private and cannot be pre-rendered, Next.js recommends using getServerSideProps(). This function allows you to fetch data on the server for each request, making it suitable for dynamic or private content that cannot be statically generated. getStaticPaths() and getStaticProps() are typically used for pre-rendering, while useEffect() is a React hook and not directly related to server-side rendering.

A significant difference between React for web and React Native is that React for web uses CSS for styling, while React Native uses JavaScript-based styles. In React Native, styles are applied using JavaScript objects, providing a more native feel and allowing for better performance and flexibility when styling components.

In React Testing Library, to find an element by its role, you can use the query findByRole(). This query is especially useful when you want to locate elements based on their accessibility roles, such as finding buttons, links, or other interactive elements. It helps ensure your tests are more accessible and accurately represent how users interact with your React components.

Immutable.js maintains data immutability by using structural sharing. When a change is made, a new object is created with the updated data, while the original data remains unchanged. This ensures immutability without the need for deep copying, making it more memory-efficient. The other options do not accurately describe how Immutable.js achieves data immutability.

The primary purpose of the React hook useState is to manage and update component state. It allows functional components to have stateful behavior, which is crucial for handling dynamic data and user interactions. The other options (create reusable components, perform API requests, and handle router navigation) are not the primary purpose of useState.

The setState method in React class components is used to update and re-render the component with new data. It's essential for managing the component's internal state and triggering re-renders when that state changes. Options 1, 3, and 4 do not accurately describe the purpose of setState.

Google Maps integration in a React application is primarily used to enhance the user interface by adding interactive maps. Developers can integrate Google Maps to display locations, directions, or any spatial data, making their applications more user-friendly and engaging. It's a common choice for applications that require geolocation features.