Top 12 interview question for a React Developer

???? French version : https://brdnicolas.com/fr/articles/12-react-interview

During React developer interviews, these questions often arise. Here’s a breakdown of each question along with simplified answers:

FUNDAMENTAL CONCEPTS

1?? What is JSX?

JSX is a javascript extension used in React that allows you to write HTML-like code within JavaScript.

2?? What is the virtual DOM?

The virtual DOM is a lightweight representation of the actual DOM in React. It helps optimize updates by comparing changes and minimizing direct DOM manipulations by grouping changes.

3?? What is a shadow DOM?

The shadow DOM is a browser feature that encapsulates styles and JavaScript within an HTML element, preventing interference with other parts of the page.

React Hooks and Optimizations:

4?? Name at least 4 hooks.

useState, useEffect, useContext, and useReducer are commonly used hooks in React for state management and side effects. But we also have useMemo, useRef, ...

5?? Why are keys important in a React element list?

keys uniquely identify elements in a list, aiding React in efficient updates and rendering.

6?? How do you optimize a React component?

Optimize components by removing redundant logic, breaking them into smaller ones, and minimizing unnecessary renders using React.memo.

Advanced React Concepts:

7?? What is the purpose of ContextAPI?

ContextAPI enables the sharing of specific data across our app, eliminating the need to pass data explicitly through each level.

8?? Do you know any design patterns? If so, which ones?

Common design patterns in React include Components, Higher Order Components (HOCs), Singleton Pattern, Observer Pattern, Factory Pattern.

My HOC article My Singleton Pattern article My Observer Pattern article

9?? What defines a pure function?

A pure function returns a value based solely on its arguments without causing side effects, making it predictable and easy to test.

React Methods and Utilities:

1??0?? What is the purpose of the map method compared to a for loop?

The map method in JavaScript is a simpler way to go through each item in an array and do something with it, like transforming each item or creating a new array based on the original one. It's easier to read and write than a for loop and often requires fewer lines of code. It's like having a special tool specifically made for working with arrays that helps you do things faster and with less code.

1??1?? What is the use of useCallback & useMemo ?

useCallback and useMemo are both tools in React that help make your app faster by optimizing how it works.

• useCallback is like a memory saver for functions. It remembers a function and only changes it when needed. Imagine you have a toy that you use often - instead of making a new one each time, you keep using the same toy until you need a different one. useCallback does that with functions in your app, so it helps to save resources and make your app quicker.
• useMemo is similar, but it's for any kind of value (not just functions) that takes time to compute. For example, suppose you're making a cake and you have some ingredients that take a while to prepare. With useMemo, once you've prepared those ingredients, you can store them and only make them again if the recipe changes. This way, you don't waste time remaking those ingredients if you don't have to. useMemo works similarly by storing values and only recalculating them if necessary, which speeds up your app.

Expert mode activated

1??2?? Explain Higher Order Components (HOCs) and provide an example of their usage.

HOCs are functions that take a component and return a new one. For instance, they can manage authentication by wrapping components with authentication logic.

Conclusion

In summary, a thorough understanding of these React concepts and tools is crucial for excelling in development interviews. Master them to shine in your React interviews.

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