In MobX, which feature allows you to track changes to your state?
- Actions.
- Decorators.
- Observables.
- Promises.
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.
How does Immutable.js ensure that data remains immutable?
- By converting all data to primitive types.
- By disallowing any updates or modifications to the data.
- By creating copies of data objects whenever updates are made.
- By using structural sharing and creating new objects for changes.
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.
In React Testing Library, to find an element by its role, you can use the query ________.
- findByAttribute
- findByElement
- findByRole
- queryByAttribute
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.
Which of the following is a key difference between styling in React for web and React Native?
- React for web requires external libraries for styling, while React Native has built-in styles.
- React for web supports responsive design, while React Native does not.
- React for web uses CSS for styling, while React Native uses JavaScript-based styles.
- React for web uses inline styles, while React Native uses external CSS files.
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.
What is the primary purpose of the React hook useState?
- To manage and update component state.
- To create reusable components.
- To perform API requests.
- To handle router navigation.
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.
You're tasked with building a PWA for a ticket booking platform. The requirement is to ensure users can view their booked tickets even when offline. How would you implement this functionality?
- a) Use local storage to store ticket data on the user's device.
- b) Implement Service Workers: Use them to intercept network requests and cache ticket data.
- c) Require users to download a PDF of their booked tickets for offline access.
- d) Use cookies to store ticket data in the user's browser.
To ensure users can view their booked tickets offline in a PWA, the best approach is to implement Service Workers (option b). Service Workers can intercept network requests, cache ticket data, and serve it to users when they are offline. Local storage (option a) is limited in capacity and may not provide a seamless offline experience. Downloading PDFs (option c) is not user-friendly, and cookies (option d) are not suitable for storing large amounts of data offline.
What is the primary benefit of using the Context API in React?
- Global state management.
- Improved performance.
- Reduced component re-rendering.
- Simplified component hierarchy.
The primary benefit of using the Context API in React is global state management. Context API allows you to create a global state that can be accessed by multiple components, eliminating the need to pass props through multiple levels of components. While it may help reduce re-renders in some cases, its primary advantage is its ability to manage global state.
You're building a modal dialog system for a web application. Which advanced React pattern would be best suited to render the modal outside the app's main DOM hierarchy, but control it from within a component?
- Context API
- Portals
- Redux
- Render Props
In this scenario, the most suitable advanced React pattern would be Portals. Portals allow you to render a component outside the normal DOM hierarchy while maintaining control over it from within a component. This is especially useful for scenarios like modals, tooltips, or popovers that need to be rendered outside the parent DOM tree. Context API, Render Props, and Redux are useful in different contexts but not specifically designed for this scenario.
A colleague is using a type any for all props in a React component. What potential issue might arise from this practice in TypeScript?
- Enhanced Performance
- Improved Code Readability
- Simplified Debugging
- Type Safety Issues
Using type any for all props in a React component can lead to potential Type Safety Issues in TypeScript. This means that TypeScript won't be able to provide compile-time checks and assistance for type-related errors, increasing the risk of runtime errors. While it may make code more flexible, it sacrifices type safety, which is a significant disadvantage in TypeScript.
What is JSX in React?
- A JavaScript XML-like syntax
- A database query language
- A style sheet language
- JavaScript eXtension
JSX stands for JavaScript XML. It allows developers to write HTML-like code within their JavaScript code. React then converts these JSX expressions into actual JavaScript objects before rendering them in the DOM.