React Js Advanced Interview Questions
Expertly Crafted React JS Interview Questions for Advanced Level Candidates
React JS is one of the most popular front-end libraries for building efficient, dynamic, and modern web applications. When it comes to interviewing for React JS roles, recruiters or hiring managers often ask advanced questions to assess a candidate's in-depth understanding of the library. These advanced interview questions may cover topics like JSX, server-side rendering, component optimization, state management, hooks, and other key concepts. Candidates should be well-versed with React JS's core principles, have a good grasp of its features and functions, and be able to apply them in real-world scenarios to excel in their React JS interviews.
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1 - How does React handle errors?
React provides a component called Error Boundary that catches any JavaScript error inside it’s tree. This allows you to display a fallback UI to the user and log the error for further debugging. Error boundaries work like a JavaScript catch {} block, but for components.
2) How to prevent a component from re-rendering?
To prevent a component from re-rendering, you can use the shouldComponentUpdate lifecycle method and compare the current props and state with the next props and state. If they are equal, then the component will not re-render. You can also use React’s PureComponent which implements shouldComponentUpdate with a shallow prop and state comparison.
3) What is the difference between a controlled and uncontrolled component?
In a controlled component, the state of the component is controlled by React. This means that the value of the input is stored in a state variable and every time it changes, the onChange event handler updates the state. In an uncontrolled component, the state is handled by the DOM itself and is accessed through a ref.
4) How do you pass data from a parent component to a child component?
Data can be passed from a parent component to a child component by using props. Props are immutable and can only be passed from parent to child, but they can be used to efficiently pass data down the component tree.
5) What is the virtual DOM in React?
The virtual DOM is a representation of the real DOM in memory. It is a data structure that stores elements, their attributes and content, and their relationships to each other. React uses the virtual DOM to efficiently update the real DOM when there are changes, instead of re-rendering the entire DOM.
6) What is the significance of keys in React?
Keys are used to give identities to elements in arrays. They help React to identify which items have changed, been added, or removed in a list. Without keys, the performance of lists rendered in React can be greatly impacted.
7) What are React Hooks?
React Hooks are functions that allow the use of state and other React features without writing a class. They were introduced in React 16.8 as a way to simplify and improve the reusability and maintainability of React components.
8) What is the purpose of useEffect in React?
The useEffect hook allows components to perform side effects after every render. This could include fetching data, updating the DOM, and subscribing to event listeners. It is a replacement for lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.
9) How do you handle forms in React?
In React, forms are handled by creating controlled components. This means that the input’s value is controlled by React through state. When a user enters something in the input, it triggers the onChange event, which updates the state and re-renders the component.
10) What are Higher-Order components in React?
Higher-Order components (HOCs) are functions that take in a component as an argument and return a new enhanced component. They are used to share common functionality or state between multiple components without having to use render props or implementing the functionality in each component separately.
11) What is Redux?
Redux is a predictable state management library for JavaScript applications. It is commonly used with React, but can also be used with other frameworks or libraries. It utilizes a single source of truth, called the store, which holds the state of the application and can be accessed by all components.
12) What are the differences between React's Props and State?
Props store data that can be passed from parent to child components, while state stores data that is managed within a component. Props are immutable and can only be changed from the parent component, while state is mutable and can be updated using setState() within the component.
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13) How do you optimize performance in React?
There are several ways to optimize performance in React, such as using React.memo() to memoize functional components, using shouldComponentUpdate or React.PureComponent to prevent unnecessary re-renders, and implementing lazy loading for components that are not immediately needed.
14) What is server-side rendering in React?
Server-side rendering is the process of rendering a web page on the server and sending it to the browser as a complete HTML page, instead of just sending JavaScript and letting the browser render the page. It allows faster initial loading of the webpage and improved SEO.
15) What is the significance of using keys in JSX?
Keys are used to identify unique elements in a collection and help React to efficiently update the DOM. When a list is rendered in React, each element is assigned a unique key, which helps React to determine which items have changed, been added, or removed. This improves the performance of the application.
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