React Portals enable rendering children into a DOM node that exists outside the DOM hierarchy of the parent component. This is useful for scenarios like modals or tooltips, where you want to render content outside the typical component hierarchy. By choosing the correct option, "Outside," you ensure that content can be rendered independently of the parent's DOM structure, providing flexibility and control in your UI design.

The MobX utility "when" can be used to create a custom reaction based on observable changes. "when" allows you to create a reaction that runs only when a specified condition is met, which can be useful for handling specific cases or side effects based on changes in observables. This utility provides fine-grained control over when reactions are triggered, beyond the automatic reactions provided by "autorun" or "computed."

The caching strategy that fetches the resource from the cache first and, if not present, then fetches it from the network is known as "Cache-First." In this strategy, the browser checks the cache for a response before making a network request. This approach helps improve website performance and load times by serving resources from the cache when available.

To make a React application work offline, you would leverage Service Workers. Service Workers enable caching of assets and allow the app to function without an internet connection by serving cached content when offline. WebSockets, REST APIs, and GraphQL are not primarily designed for offline functionality but rather for real-time communication and data retrieval.

One potential downside of the current React diffing algorithm is that it can lead to excessive virtual DOM updates in some cases. If component updates are frequent or the tree structure is complex, React may perform more updates than necessary, affecting performance. Developers need to be mindful of optimizing their components and key assignments to mitigate this limitation and improve React app performance.

Stateless components in React are also known as Functional Components. These components are defined as JavaScript functions and do not have internal state management. They receive props and render content based on those props. The other options do not accurately describe stateless components.

React Portals are commonly used to render modals outside the main DOM hierarchy. This is especially useful for rendering elements like modals, which need to float above the main application content but may have complex structures.

To connect a React component to the Redux store, one commonly uses the mapStateToProps function. This function maps the state from the Redux store to the props of the connected component, allowing it to access and display the state data. It's an essential part of integrating Redux with React for state management.

When making API calls using Axios, you can handle errors by using the catch() method to catch any errors that occur during the request. Axios will reject the promise if the request encounters an error, allowing you to handle the error condition and take appropriate actions. Throwing an exception or returning an empty response are not standard error-handling practices in Axios.

To prevent shared code from being loaded multiple times, you should use Webpack's code splitting with dynamic imports to create a shared bundle. This ensures that the shared code is loaded once and reused across routes as needed. Combining code into a single file doesn't achieve code separation and may result in larger bundles. Loading via CDN and server-side rendering address different issues.