To make properties recompute only when the data they depend upon changes, you use the @computed decorator in MobX. This decorator creates a computed property, which automatically updates itself when the observed data changes. The other decorators (@action, @observer, @autorun) serve different purposes and do not create computed properties.

Redux's primary role in a React application is to manage global state. It provides a centralized store for application data that can be accessed by different components. While the other options are important aspects of a React application, such as rendering, styling, and routing, they are not the primary role of Redux.

In React Router, the Route component is primarily used to define a specific path and its corresponding component. When a user navigates to a specified URL path, the associated component is rendered. This is fundamental for setting up routing in a React application using React Router.

In React Router, the component is used to create links to different parts of the application. It allows users to navigate between different views or components without a full page reload. The other options, such as , , and , serve different purposes in routing.

In React, the key attribute is used during the diffing process to identify which items in a list have changed. The key prop helps React efficiently update the UI by associating elements with their previous versions, ensuring that only the necessary changes are applied.

Implementing a cache-first strategy in service workers requires the use of the Cache-Control HTTP header with directives like public and max-age. By specifying public, you allow the response to be cached, and max-age sets the maximum time that the response should be considered fresh. This strategy ensures that the service worker prioritizes cached responses over network requests when possible, enhancing performance and offline capabilities.

To enhance the performance of a Redux-connected component when its state changes frequently, you can use memoization techniques like Reselect to optimize mapStateToProps. Reselect helps prevent unnecessary re-renders by caching the results of expensive calculations based on the state. Increasing the use of Redux Thunk middleware or using a higher-order component (HOC) isn't directly related to optimizing component performance. Redux middleware for caching is not a common approach for this purpose.

Webpack facilitates lazy loading of code chunks in an application through code splitting and dynamic imports. It allows developers to break down their application into smaller code chunks that can be loaded on-demand, reducing the initial load time and improving performance. The other options are not accurate representations of how Webpack enables lazy loading.

When working with WebSockets in React, the Socket.io library provides a convenient way to establish and manage socket connections. Socket.io is a popular library that offers real-time, bidirectional communication between clients and the server, making it a common choice for WebSocket functionality in React applications. Express.js is a server-side framework, Redux-WebSocket doesn't handle WebSocket connections directly, and Axios is used for making HTTP requests.

To create a new Web Worker, you typically use the Worker() constructor in JavaScript. This constructor is responsible for creating a new worker that can run JavaScript code in the background. The other options are not the correct constructor names for creating Web Workers.