Front-End Developer Interview Questions (2024)

Frontend Development involves creating the user interface (UI) of web pages. It focuses on presenting the data received from the backend in an interactive and user-friendly manner. The UI is crucial in attracting users, and organizing elements interactively and attractively across various devices is the essence of Frontend Development. As dynamic and responsive web applications have become more prevalent, the demand for skilled front-end developers has surged. Companies like Google, Facebook, Netflix, LinkedIn, and many others depend on expert front-end developers to build and maintain their user-facing applications because of the language’s flexibility, robustness, and performance.

In this article, we will present top Frontend Developer interview questions designed for both beginners and experienced professionals. Frontend Development encompasses various technologies like HTML, CSS, JavaScript, and frameworks such as ReactJS. We have compiled a thorough list of Frontend Developer interview questions, covering a range of topics from basic to advanced levels. Whether you are a beginner or an expert in Frontend Development, these interview questions will help you excel in your upcoming MERN interviews.

Front-End Developer Interview Questions and Answers for Freshers

1. What is the purpose of the doctype declaration?

The purpose of the doctype declaration is to tell the web browser what version of HTML you are using, so it can render the page correctly. It’s the very first thing at the top of your HTML document. For example, <!DOCTYPE html> is used for HTML5.

2. Explain the difference between <div> and <span>

The <div> and <span> elements are both used to group content, but they serve different purposes:

<div>: This is a block-level element, which means it takes up the full width available and starts on a new line. It’s used to group larger sections of content and apply styles or layout properties to them. For example, you might use <div> to wrap entire paragraphs, images, or other block-level elements.
<span>: This is an inline element, meaning it only takes up as much width as necessary and doesn’t start on a new line. It’s used to group smaller pieces of content within a block-level element, like words or phrases, so you can style them individually without affecting the layout of the entire block. For example, you might use <span> to change the color of a specific word in a sentence.

3. Define HTML meta tags.

HTML meta tags are small pieces of information in the <head> of an HTML document. They don’t show up on the page but give important info to browsers and search engines.

<meta charset="UTF-8">: Sets the character encoding.
<meta name="description" content="description here">: Gives a summary of the page.
<meta name="keywords" content="keywords here">: Lists important keywords.
<meta name="viewport" content="width=device-width, initial-scale=1.0">: Makes the page responsive for mobile devices.

4. What is the box model in CSS?

The box model in CSS describes how elements are structured and displayed. It includes:

Content: The actual content inside the element (text, images, etc.).
Padding: The space between the content and the border.
Border: The line around the padding and content.
Margin: The space outside the border, creating distance between elements.

This model helps in controlling the layout and spacing of elements on a web page.

5. Describe the difference between margin and padding.

Padding: This is the space inside the border of an element, between the element’s content (like text or images) and its border. It pushes the content away from the edges of the element, making the content area larger without affecting the space around the element.
Margin: This is the space outside the border of an element, creating a gap between the element and other elements or the edge of the container. It moves the entire element away from surrounding elements, affecting the layout and spacing between elements on the page.

In summary, padding controls the space inside the element, while margin controls the space outside the element.

6. What is the importance of media queries in responsive design?

Media queries are essential in responsive design as they allow you to apply different CSS styles based on the characteristics of the user’s device, such as screen size, resolution, orientation, etc. This ensures that the web content looks good and is usable on all devices, from desktops to tablets to smartphones.

7. Describe the difference between em and rem units in CSS.

Both em and rem are relative units in CSS. The em unit is relative to the font size of its closest parent element, while the rem unit is relative to the root element’s font size. This makes rem units more predictable and consistent across different elements, whereas em units can accumulate and become complex when nested.

8. What is the flexbox model, and what is justify-content and align items in flex box?

The flexbox model is a layout system in CSS designed to provide a more efficient way to align and distribute space among items in a container. It allows for responsive elements to adjust and distribute space within a container, even when the size of items is unknown or dynamic. Flexbox is particularly useful for creating complex layouts with simple, clean code.

Explain the purpose of justify-content and align-items in flexbox.

justify-content: This property aligns flex items along the main axis (horizontal by default). It controls the distribution of space between and around content items.
align-items: This property aligns flex items along the cross axis (vertical by default). It determines how flex items are aligned within the flex container.

9. How does CSS Grid differ from Flexbox?

CSS Grid is a two-dimensional layout system that handles both rows and columns, whereas Flexbox is a one-dimensional system focusing on either rows or columns at a time. CSS Grid is more powerful for creating complex, grid-based layouts, while Flexbox is more suitable for simpler, single-axis alignments.

10. Explain the use of the grid-template-columns property.

The grid-template-columns property defines the columns of a grid container by specifying the width of each column. You can set fixed, flexible, or auto-sized column widths, making it easy to create responsive and adaptive grid layouts.

11. Explain the concept of hoisting in JavaScript.

In JavaScript, hoisting is a behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase, before the code is executed. Here’s how it works:

Variable Hoisting: Only the declaration part of var variables is hoisted to the top, not the initialization. For example:

console.log(x); // undefined
var x = 5;

This code is treated as:

var x;
console.log(x); // undefined
x = 5;

Function Hoisting: Function declarations are fully hoisted, meaning both the function’s name and its body are available before the function is called. For example:

greet(); // "Hello" 
function greet() { 
console.log("Hello"); 
}

This code works because the function declaration is hoisted, allowing greet to be called before its definition.

12. What is the difference between let, const, and var?

JavaScript var keyword

The var is the oldest keyword to declare a variable in JavaScript. It has the Global scoped or function scoped which means variables defined outside the function can be accessed globally, and variables defined inside a particular function can be accessed within the function.

var a = 10
function f() {
var b = 20
console.log(a, b)
}
f();
console.log(a);

Output

10 20 10

JavaScript let keyword

The let keyword is an improved version of the var keyword It is introduced in the ES6 or EcmaScript 2015. These variables has the block scope. It can’t be accessible outside the particular code block ({block}).

let a = 10;
function f() {
let b = 9
console.log(b);
console.log(a);
}
f();

Output

9 10

JavaScript const

The const keyword has all the properties that are the same as the let keyword, except the user cannot update it and have to assign it with a value at the time of declaration. These variables also have the block scope. It is mainly used to create constant variables whose values can not be changed once they are initialized with a value.

const a = 10;
function f() {
a = 9
console.log(a)
}
f()

13. What is a closure in JavaScript?

A closure in JavaScript is a function that keeps access to its outer function’s variables, even after the outer function has finished running. It’s like the function has a memory of its surroundings.

14. Explain the differences between arrow functions and regular functions.

Arrow Functions:- The arrow functions is one of the features introduced in the ES6 Version of javascript. It allows us to create functions in a cleaner way compared to regular functions.

Regular Functions:- Regular functions in JavaScript are the traditional way to define functions. They can be used for a wide range of tasks, from simple calculations to complex operations. Here’s a deeper look at regular functions

15. How does event delegation work in the DOM?

Event delegation is a technique where a single event listener is added to a parent element instead of multiple event listeners to individual child elements. When an event occurs, it propagates (bubbles) up the DOM tree, and the event listener on the parent can handle events triggered by its children. This improves performance and simplifies code management.

16. Explain the purpose of the data- attributes.

The data- attributes are used to store custom data directly on HTML elements. These attributes allow developers to embed extra information within elements without needing to create custom properties or use JavaScript. They are particularly useful for storing data that needs to be accessed later via JavaScript.

17. What is AJAX, and how does it work?

AJAX (Asynchronous JavaScript and XML) is a technique for creating fast and dynamic web pages by allowing web applications to send and retrieve data from a server asynchronously without interfering with the display and behavior of the existing page. It works by using the XMLHttpRequest object to communicate with the server.

18. Explain the role of the XMLHttpRequest object.

The XMLHttpRequest object is used to interact with servers. It allows you to send HTTP or HTTPS requests to a web server and load the server response data directly into the script. This enables the retrieval of data without refreshing the entire web page.

19. What is REST, and how does it differ from SOAP?

REST (Representational State Transfer) is an architectural style for designing networked applications. It uses standard HTTP methods (GET, POST, PUT, DELETE) and is known for its simplicity and scalability. SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in web services, known for its robustness and security features. REST is typically faster and easier to use than SOAP.

20. Describe the common HTTP methods used in RESTful APIs.

GET: Retrieves data from the server.
POST: Sends new data to the server.
PUT: Updates existing data on the server.
DELETE: Removes data from the server.

21. What is ReactJS?

ReactJS is a popular JavaScript library for building user interfaces, particularly single-page applications. Developed by Facebook, React allows developers to create reusable UI components that manage their own state. It uses a virtual DOM to efficiently update the real DOM, providing a responsive and dynamic user experience.

22. What is JSX in React?

JSX (JavaScript XML) is a syntax extension for JavaScript used in React to describe what the UI should look like. It allows you to write HTML structures in the same file as JavaScript code, making it easier to understand and manage the component structure.

23. Explain the purpose of state in React components.

State is an object that holds data that may change over the lifecycle of a React component. It allows components to manage and render dynamic data, providing interactivity and real-time updates in the UI.

24. Differentiate between functional and class components in React.

Functional components are simple JavaScript functions that return JSX. They do not have their own state or lifecycle methods but can use React hooks.
Class components are ES6 classes that extend from React.Component. They can have state and lifecycle methods, making them more powerful but also more complex.

25. Explain the use of the useState hook in React.

The useState hook allows you to add state to functional components. It returns an array with the current state value and a function to update it, enabling functional components to manage state and re-render when the state changes.

26. What is the useEffect hook, and why is it used?

The useEffect hook allows you to perform side effects in functional components, such as data fetching, subscriptions, or manually changing the DOM. It runs after every render by default, but you can control its execution by providing dependencies.

27. What is the difference between props and state?

Props: Props (short for properties) are used to pass data from one component to another. They are read-only and cannot be modified by the receiving component.
State: State is used to manage data that changes over time within a component. State is mutable and can be updated using the setState function in class components or the useState hook in functional components.

28. What are props?

Props are a way to pass data from parent components to child components in React. They allow you to dynamically configure child components and make them reusable. Props are immutable, meaning that once a prop is passed to a component, it cannot be changed by that component.

29. What are React hooks?

React hooks are functions that let you use state and other React features in functional components. Introduced in React 16.8, hooks allow you to use features like state, lifecycle methods, and context without writing class components. Some commonly used hooks are useState, useEffect, and useContext.

30. What are custom hooks?

Custom hooks are JavaScript functions that allow you to reuse stateful logic across multiple components. They enable you to extract and share logic without duplicating code. Custom hooks start with the prefix “use” and can utilize other hooks within them.

31. What is the virtual DOM?

The virtual DOM (VDOM) is an in-memory representation of the real DOM elements generated by React components. React uses the virtual DOM to optimize rendering by updating only the parts of the real DOM that have changed. This makes updates faster and more efficient.

32. What are the features of React?

Component-Based Architecture: Build encapsulated components that manage their own state and compose them to make complex UIs.
Virtual DOM: Efficiently updates and renders only the components that change, improving performance.
JSX: A syntax extension that allows you to write HTML-like code within JavaScript.
Unidirectional Data Flow: Data flows in one direction, making it easier to understand and debug the application.
Hooks: Functions that allow you to use state and other React features in functional components.
Declarative: Describe what you want the UI to look like, and React handles the rendering.
React Native: Enables the use of React for building mobile applications.

33. What problem does Redux solve in a React application?

Redux is a state management library that helps manage and centralize application state. It solves problems related to state sharing and consistency, making it easier to manage complex state logic and enabling a predictable state flow through actions and reducers.

34. Explain the roles of actions, reducers, and the store in Redux.

Actions: Plain JavaScript objects that describe what happened in the app.
Reducers: Pure functions that take the current state and an action and return a new state.
Store: Holds the application state and allows access to state, dispatching actions, and registering listeners.

35. How can you optimize website performance?

Minimize HTTP requests by combining files.
Use asynchronous loading for CSS and JavaScript.
Optimize images and use modern formats.
Enable browser caching.
Minify CSS, JavaScript, and HTML.
Use a Content Delivery Network (CDN).

36. Explain lazy loading and its benefits.

Lazy loading is a technique where content, especially images or iframes, is only loaded when it is needed, such as when it comes into the viewport. This reduces initial load time, saves bandwidth, and improves performance by loading only the necessary content.

37. What is CORS, and how does it work?

CORS (Cross-Origin Resource Sharing) is a security feature implemented by browsers to allow or restrict web pages from making requests to a different domain than the one that served the web page. It works by using HTTP headers to indicate whether a resource can be accessed by a web page from a different origin.

38. What is Webpack, and how does it improve the frontend development workflow?

Webpack is a module bundler for JavaScript applications. It takes modules with dependencies and generates static assets representing those modules. It improves the frontend development workflow by bundling, minifying, and optimizing assets, enabling hot module replacement, and simplifying the management of dependencies.

39. Explain the concept of code splitting in Webpack.

Code splitting is a technique where the code is split into smaller bundles that can be loaded on demand. This reduces the initial load time and improves performance by loading only the necessary code when it is needed. Webpack enables code splitting through dynamic import() statements and configuration options.

40. Describe the differences between unit testing and integration testing.

Unit Testing: Focuses on testing individual components or functions in isolation to ensure they work as expected.
Integration Testing: Tests the interaction between different components or systems to ensure they work together correctly. It verifies that integrated parts of an application function as a whole.