You are optimizing a large list where each item has its own click handler. Instead of attaching handlers to each item, you want to improve performance. What approach should you take?

  • Implement event delegation by attaching a single event handler to a common ancestor of the list items.
  • Use inline event handlers for each list item.
  • Create a separate component for each list item.
  • Increase the size of the click area for each list item.
To improve performance when dealing with a large list of items, each with its own click handler, you should implement event delegation. This involves attaching a single event handler to a common ancestor of the list items. This way, you can handle all click events efficiently without the overhead of attaching individual handlers to each item. The other options are not effective performance optimization strategies in this context.

In React Transition Group, what prop is used to define the duration of an exit animation?

  • transitionDuration
  • animationDuration
  • exitDuration
  • duration
In React Transition Group, the prop used to define the duration of an exit animation is exitDuration. This prop allows you to control how long it takes for a component to animate out of the view when it's being removed. The other options (transitionDuration, animationDuration, and duration) are not specific to exit animations in React Transition Group.

How can you ensure a component does not re-render unnecessarily when consuming a context?

  • Using memoization techniques like React.memo().
  • Implementing context with useState.
  • Wrapping the component with React.StrictMode.
  • Increasing the component's complexity.
To prevent unnecessary re-renders when consuming context, you can use memoization techniques like React.memo(). This higher-order component wraps the component and only re-renders it when its props or context values change. It's a performance optimization technique to avoid unnecessary re-renders, especially when the component depends on context values. The other options are not related to preventing re-renders due to context consumption.

In a MobX-powered e-commerce application, you want to ensure that the cart total is automatically updated whenever an item is added or its quantity is changed. Which approach would you use to achieve this efficient update?

  • Actions
  • Computed Properties
  • Observables
  • Reactions
To achieve an efficient update of the cart total in response to changes in items or their quantities, you would use Reactions in MobX. Reactions are triggered automatically when observable data they depend on changes. In this case, a reaction can recalculate the cart total whenever the cart items or their quantities change, ensuring an automatic and efficient update.

What happens if you modify an observable outside of an action in strict mode in MobX?

  • A warning is issued, but the modification is applied.
  • An error is thrown.
  • No effect, it's allowed in strict mode.
  • The modification is automatically batched.
In MobX strict mode, modifying an observable outside of an action results in an error being thrown. This is a fundamental principle to ensure that state changes are predictable and follow clear patterns. It helps prevent unintentional side effects and maintains the reactivity system's integrity.

What considerations should be taken into account when deciding the expiration time for cached assets in a PWA?

  • Network latency, asset size, and the frequency of updates.
  • The browser's cache size, the user's device type, and CPU usage.
  • The popularity of the asset, the development team's preferences, and the server's load.
  • The user's geolocation, the asset's file type, and the project budget.
When deciding the expiration time for cached assets in a Progressive Web App (PWA), several factors must be considered, including network latency (which affects download times), asset size (as larger assets take longer to download), and the frequency of updates (more frequent updates may require shorter cache times to ensure users receive the latest content). These considerations impact the user experience and performance of the PWA.

In terms of security, what is an essential consideration when integrating third-party authentication providers?

  • Enforcing multi-factor authentication (MFA).
  • Sharing API keys and secrets in public repositories.
  • Storing user credentials on the client-side.
  • Validating user input before sending it to the provider.
When integrating third-party authentication providers, it's crucial to validate user input before sending it to the provider. This helps prevent security vulnerabilities like injection attacks. Storing user credentials on the client-side, sharing secrets in public repositories, and not enforcing MFA can all lead to security issues, but proper input validation is a fundamental security practice.

When you want to terminate a Web Worker from the main thread, you call the ________ method.

  • terminate()
  • end()
  • stop()
  • close()
To terminate a Web Worker from the main thread, you call the terminate() method. This method stops the execution of the worker thread. The other options are not the correct methods for terminating a Web Worker from the main thread.

What is the main advantage of using Render Props over Higher Order Components (HOCs) in React?

  • Better performance and rendering speed.
  • Improved component reusability and composability.
  • Simplicity and ease of use.
  • Stronger typing and static analysis.
The main advantage of using Render Props over Higher Order Components (HOCs) in React is improved component reusability and composability. Render Props make it easier to share logic between components and are more flexible than HOCs, which can lead to more maintainable and readable code. While HOCs have their own benefits, they may not offer the same level of flexibility as Render Props.

In React-Redux, the hook that allows you to extract data from the Redux store is ________.

  • connect
  • mapDispatchToProps
  • useEffect
  • useSelector
In React-Redux, the hook used to extract data from the Redux store is useSelector. This hook allows you to select data from the store's state and use it in your components. mapDispatchToProps is used for dispatching actions, connect is a higher-order component for connecting React components to the store, and useEffect is used for side effects.