“Top Frontend Interview Questions : (Part 3) — Boost Your Knowledge and Ace Your Next Job Interview!”

Ashwini Paraye
5 min readJun 6, 2023

In this article, we will cover important frontend interview topics including Redux, higher-order components (HOCs), React lifecycle methods, form handling, React hooks, React Router, and performance optimization. Prepare yourself with these essential concepts to excel in your next job interview. Let’s dive in and enhance your frontend knowledge!

1. How does redux works :

  • Redux is a state management library for JavaScript applications.
  • It works by maintaining a centralized store that holds the application state.
  • Components can dispatch actions to modify the state, and reducers handle these actions to update the state.
  • The updated state is then propagated back to the components, triggering re-renders and ensuring consistent data flow throughout the application.

2. What are higher-order components (HOCs) in React and how do they work? :

  • Higher-order components (HOCs) are a pattern in React that allows you to reuse component logic.
  • They are functions that take a component as input and return a new enhanced component.
  • HOCs enable you to add additional functionality or modify the behavior of a component without changing its original code.
  • Think of HOCs as wrappers around components, providing them with extra powers or abilities.

3. Lifecycle methods of React.js :

Lifecycle methods in React.js are special functions that are called at different stages of a component’s lifecycle. They allow you to perform specific actions or implement logic at key points during the component’s existence. Here’s a brief explanation of some commonly used lifecycle methods:

  • componentDidMount : This method is called immediately after a component is rendered for the first time. It’s often used for initializing data or making API calls.
  • componentDidUpdate : This method is triggered when a component’s state or props change. It allows you to update the component or perform additional actions based on the changes.
  • componentWillUnmount : This method is called right before a component is removed from the DOM. It’s used for cleaning up resources, such as canceling timers or unsubscribing from event listeners.

4. How do you handle lifecycle methods in functional component :

  • In functional components, we handle lifecycle methods using the useEffect hook in React.
  • The useEffect hook allows us to perform side effects and mimic the behavior of lifecycle methods.
  • By specifying dependencies, we can control when the effect runs. For example, we can run code when the component mounts, updates, or unmounts, similar to componentDidMount, componentDidUpdate, and componentWillUnmount in class components.
  • This way, we can manage state, fetch data, or perform any necessary cleanup in a functional component’s lifecycle.

5. What are controlled components in React? :

  • Controlled components in React are input elements (such as text fields, checkboxes, or radio buttons) whose values are controlled by React state.
  • This means that the value of a controlled component is stored in the component’s state, and any changes to the value are handled through state updates.
  • This allows React to have full control over the component’s behavior, making it easy to validate, manipulate, and synchronize the component’s value with other parts of the application.

6. How do you handle forms in React? :

Handling forms in React involves capturing user input, managing state, and responding to form submissions. Here’s a simplified explanation:

  • Capturing User Input : Use React state to store the values entered by the user in form inputs such as text fields, checkboxes, or dropdowns. Update the state as the user types or selects options.
  • Managing State : Bind the form inputs to their corresponding state values using the value attribute and provide event handlers (onChange, onSubmit, etc.) to update the state as the user interacts with the form.
  • Responding to Form Submissions : Handle the form submission event by attaching an onSubmit handler to the form element. In the handler function, access the form data from the state and perform necessary actions like validation, sending data to a server, or displaying a success message.

7. Explain the concept of React hooks and provide examples of a few commonly used hooks :

React hooks are functions that allow you to use state and other React features in functional components. They simplify the management of stateful logic and side effects. Here are a few commonly used hooks:

  • useState: Allows you to add state to functional components. For example, you can use useState to track a counter’s value and update it.
  • useEffect: Handles side effects, such as fetching data or subscribing to events. It runs after rendering and can be used to perform cleanup tasks.
  • useContext: Accesses a React context, allowing you to share data across components without prop drilling. It simplifies global state management.
  • useRef: Creates a mutable value that persists across renders. It can be used to reference DOM elements or store any mutable value without causing re-renders.

8. What is React Router? :

  • React Router is a popular library in React.js that allows you to handle routing and navigation in your web applications.
  • It provides a way to create different routes, such as URLs, for different components or pages in your application.
  • With React Router, you can define routes, handle navigation between pages, pass parameters to components, and even implement features like nested routing.
  • It simplifies the process of building single-page applications by managing the application’s URL and rendering the appropriate components based on the current URL.

9. How would you optimize the performance of a React application? :

  • Use shouldComponentUpdate/React.memo to prevent unnecessary re-renders.
  • Assign unique key props for list items to efficiently update and re-render lists.
  • Split code into smaller chunks and load on-demand for faster initial load time.
  • Optimize image loading by compressing and lazy loading non-visible images.
  • Implement caching, use appropriate HTTP headers, and minimize unnecessary API calls.
  • Memoize expensive calculations using techniques like React’s useMemo.
  • Avoid unnecessary state updates, use setState callbacks, and functional updates.
  • Deploy using React’s production build for built-in performance optimizations.

In conclusion, mastering React.js concepts is crucial for acing interviews. By embracing commonly asked questions and grasping underlying principles, you’ll boost your chances of success. Best of luck in your interviews, and remember to approach them with confidence and genuine understanding!

I hope you found this article helpful. Thank you for reading! 😀

Happy Coding !

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Ashwini Paraye

Fullstack Developer | 👨‍💻 Writing about programming concepts | React.js | JavaScript | Vue.js | Golang