When would you use useRef?

React Hooks Interview Questions and Answers

Let’s discuss some common questions that you should prepare for the interviews. These questions will help clear the interviews, specially for the frontend development or full stack development role....

1. What is React Hooks?

React Hooks is a function that lets you use state and other React features without writing a class. They were introduced in React 16.8 to enable functional components to use state which means to make the code good and easy to understand....

2. What problems do React Hooks solve?

React Hooks solves the problems of sharing the stateful logic between components in a more modular and reusable way than class component....

3. What are the basic built-in React Hooks?

The basic built-in React Hooks are useState, useEffect, useContext, useReducer, useCallback, useMomo, useRef and useImperativeHandle....

4. How does useState work?

The useState Hook enables you to add state to your functional components. It returns a stateful value and a function that can be used to update that value. By using Hooks, you can extract stateful logic from your component, which can then be tested independently....

5. When would you use useEffect?

useEffect is typically used in React functional components to perform side effects, like data fetching, subscriptions, or DOM manipulations, after the component has rendered. It’s similar to lifecycle methods in class components, but it’s more flexible and concise....

6. What is the purpose of useCallback Hooks?

The purpose of useCallback Hooks is used to memoize functions, and prevent unnecessary re-rendering of child components that rely on those components. The useCallback function in React is mainly used to keep a reference to a function constant across multiple re-renders. This feature becomes useful when you want to prevent the unnecessary re-creation of functions, especially when you need to pass them as dependencies to other hooks such as useMemo or useEffect....

7. Explain the difference between useMemo and useCallback?

Here’s a difference of useMemo and useCallback int tabular form:...

8. What is the useContext used for?

useContext is a function that enables access to context values provided by a Context.Provider component at a higher level in the component tree. This allows data to be passed down the tree without the need to manually pass props at each level....

9. How does useReducer differ from useState?

useState useReducer Handles state with a single value Handles state with more complex logic and multiple values Simple to use, suitable for basic state needs More complex, suitable for managing complex state logic Simple state updates, like toggles or counters Managing state with complex transitions and logic Directly updates state with a new value Updates state based on dispatched actions and logic Not used Requires a reducer function to determine state changes Logic is dispersed where state is used Logic is centralized within the reducer function...

10. What is useEffect Hooks?

useEffect Hooks is used to connect component to an external system. In this the depenedeny array specifies when the effect should run based on changes in its dependencies and when the dependency array is absent in useEffect, the effect will run after every render....

11. When would you use useRef?

useRef is used in React functional components when you need to keep a mutable value around across renders without triggering a re-render. It’s commonly used for accessing DOM elements, caching values, or storing mutable variables. You can use useRef to manage focus within your components, such as focusing on a specific input element when a condition is met without triggering re-renders....

12. Explain the purpose of useLayoutEffect?

useLayoutEffect is similar to useEffect but fires synchronously after all DOM mutations. It’s useful for reading from the DOM or performing animations before the browser paints. Due to its synchronous nature, excessive usage of useLayoutEffect may potentially impact performance, especially if the logic within it is computationally intensive or blocking. It’s essential to use useLayoutEffect judiciously and consider performance implications carefully....

13. What is Custom Hooks?

Custom hooks in React are like your own personal tools that you can create to make building components easier. They’re functions you write to do specific tasks, and then you can reuse them in different components. They’re handy because they let you keep your code organized and share logic between different parts of your application without repeating yourself....

14. How do you create a custom Hook?

Here is to creating a custom Hooks step-by-step....

15. What is the benefit of using custom Hooks?

The benefits of using custom hooks in React include code reusability, separation of concerns, abstraction of complex logic, improved testability, and the ability to compose hooks together for flexible and scalable code. They help in maintaining a clear separation between presentation and business logic, making it easier to reason about and maintain your codebase as it grows....

16. Can custom Hooks accept parameters?

Yes, custom hooks in React can indeed accept parameters. By accepting parameters, custom hooks become more flexible and can adapt their behavior based on the specific needs of different components....

17. How do you share code between custom Hooks?

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18. What are the rules of Hooks?

To share code between custom hooks in React, you can simply create regular JavaScript functions or utility functions and import them into your custom hooks as needed. These shared functions can encapsulate common logic or helper functions that are used across multiple custom hooks....

19. How do you conditionally run effects with useEffect?

The rules of Hooks are:...

20. What happens if you omit dependencies in the dependency array of useEffect?

To conditionally run effects with useEffect in React, you can use the dependency array as the second argument to specify the values that the effect depends on. By updating these dependencies, you can control when the effect should run....

21. How do you fetch data with useEffect?

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22. What is the purpose of the second argument in useState?

If you omit dependencies in the dependency array of useEffect, the effect will run after every render. This means that the effect will be executed on the initial render and after every subsequent re-render, regardless of whether any specific values have changed....

23. Explain the concept of lazy initialization with useState?

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24. What are the benefits of using React.memo?

You can fetch data with useEffect in React by performing the data fetching operation inside the effect function. Typically, you use asynchronous functions like fetch to make HTTP requests to an API endpoint and update the component state with the fetched data....

25. How do you test components that use Hooks?

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26. Can you use Hooks in class components?

The purpose of the second argument in useState is to initialize the state value. When you call useState(initialValue), the initialValue provided as the second argument is used to initialize the state variable....

27. How do you handle forms with Hooks?

Lazy initialization with useState allows you to initialize state lazily based on a function, which is only called on the initial render. The concept of lazy initialization with useState in React allows you to initialize state lazily, i.e., on-demand when it’s needed, rather than eagerly during component initialization. This means that you can compute the initial state dynamically based on some conditions or heavy computations....

28. What is the purpose of the useImperativeHandle Hook?

React.memo is a higher-order component provided by React that can be used to optimize functional components by memoizing them. The benefits of using React.memo include improved performance by memoizing component renders based on props, reduced re-renders, enhanced component reusability, and simplified optimization without manual memoization logic....

29. How do you share state logic between components?

You can test components that use hooks in React using testing libraries like @testing-library/react or enzyme. Write test cases to simulate component rendering, user interactions, and expected outcomes. Use testing utilities like render, fireEvent, and expect to interact with components and assert their behavior, ensuring hooks are working correctly....

30. What are some common patterns for using custom Hooks?

No, you cannot use hooks in class components directly. Hooks are a feature introduced in React 16.8 to allow stateful logic to be used in functional components. They cannot be used in class components because hooks rely on the functional component’s call order to manage state and lifecycle behaviors, which is not compatible with the class component’s lifecycle methods....