When profiling a React application using React DevTools, what color indicates a component that has re-rendered?

  • Blue
  • Green
  • Red
  • Yellow
When profiling a React application using React DevTools, a component that has re-rendered is indicated by the color Red. This visual cue helps developers identify components that are re-rendering, which can be useful for optimizing performance by reducing unnecessary renders. The other colors are not typically associated with indicating re-renders in React DevTools.

When using Render Props, what is the typical method of passing data back to the parent component?

  • Callback function
  • Redux
  • Context API
  • Component state management (e.g., useState)
When using Render Props, the typical method of passing data back to the parent component is through a callback function. The child component that receives the Render Prop invokes this callback function with the data that needs to be passed to the parent component. This callback mechanism facilitates communication between the parent and child components, allowing data to flow from child to parent. The other options are not the typical way to pass data back in this context.

The ________ library in React is popular for creating responsive and interactive charts.

  • React Graph
  • React Charts
  • Recharts
  • Chart.js
The "Recharts" library is popular in the React community for creating responsive and interactive charts. It offers a simple and declarative API for building charts within React applications. While other chart libraries can be used, Recharts is known for its ease of use and customization options. The other options are not as closely associated with React charting.

In a project, you're required to fetch data from multiple REST endpoints simultaneously and display it only when all the data is available. Which Axios method would be most suitable for this?

  • Axios.all()
  • Axios.concurrent()
  • Axios.parallel()
  • Axios.series()
To fetch data from multiple REST endpoints simultaneously and wait for all the data to be available before proceeding, you should use 'Axios.all()' to make multiple requests concurrently. 'Axios.parallel()' and 'Axios.concurrent()' are not standard Axios methods, and 'Axios.series()' would make requests sequentially, not concurrently.

In the context of React, why can immutability lead to more efficient rendering?

  • It causes more memory leaks.
  • It increases the component's complexity.
  • It reduces the need for virtual DOM diffing.
  • It slows down the rendering process.
Immutability in React can lead to more efficient rendering because it reduces the need for virtual DOM diffing. When the state or props of a component are immutable, React can easily compare the previous and current values to determine what parts of the DOM need to be updated. This optimization can significantly improve the performance of React applications by minimizing unnecessary re-renders.

What is the primary benefit of using TypeScript with React?

  • Enhanced code readability and maintainability.
  • Faster rendering of React components.
  • Improved integration with third-party libraries.
  • Automatic code deployment to production servers.
The primary benefit of using TypeScript with React is enhanced code readability and maintainability. TypeScript provides static typing, which helps catch errors at compile time and provides better IntelliSense support. This leads to more robust and maintainable code. While the other options might be desirable in different contexts, they are not the primary benefit of using TypeScript with React.

Which of the following describes React Native?

  • A hybrid mobile app development framework.
  • A native mobile app development platform.
  • A popular JavaScript framework for web apps.
  • A programming language for server-side scripting.
React Native is a hybrid mobile app development framework. It allows developers to build mobile applications for multiple platforms (e.g., iOS and Android) using a single codebase in JavaScript and React. While React Native uses native components, it is distinct from native development platforms.

When a functional component's output is not affected by changes in props, you can wrap it with ________ to memoize its rendered output.

  • React.memo
  • ReactDOM
  • useEffect
  • useState
You can wrap a functional component with the React.memo higher-order component to memoize its rendered output. Memoization is used to optimize functional components by preventing unnecessary renders when the input props do not change. It's particularly useful when dealing with performance-critical components that should only re-render when their props change.

The lifecycle method that runs immediately after a component's output is rendered to the DOM is ________.

  • componentDidMount
  • componentDidUpdate
  • componentWillMount
  • componentWillUnmount
The lifecycle method that runs immediately after a component's output is rendered to the DOM in React is componentDidMount. This is where you can perform actions that require interaction with the DOM, like setting up timers or fetching data from an API.

The main purpose of the Render Props pattern is to allow for ________ between components.

  • communication
  • data sharing
  • isolation
  • state management
The primary purpose of the Render Props pattern is to allow for communication between components. It enables components to share data or logic in a flexible way, making it a powerful technique for building reusable and composable components. With Render Props, components can communicate and pass information, enhancing the flexibility and reusability of the code.