Are you preparing for your next big front-end development opportunity? While the world of technical interviews can be tough to navigate, it is possible with the right advice.
To crack your next interview, read our comprehensive guide article on interview questions for front-end developers. This three-part guide, which consists of 30 carefully selected questions at beginner, intermediate, and advanced levels, ensures that there is something for everyone, regardless of whether you are just starting or want to hone your skills.
Jump right in to enhance your skills, boost your self-esteem, and ace your next interview!
Interview Questions for Front-End Developers
Beginner Level Questions
What is HTML?
HTML stands for HyperText Markup Language and is the common markup language to develop web pages. Using a set of components and tags, it describes the structure and content of web pages. HTML lets developers arrange material in a web browser, thus constructing the overall skeleton of a website based on the specifications of how this material should be arranged and presented.
What are CSS selectors?
CSS stands for Cascading Style Sheets, and selectors are patterns that are used to style HTML elements. They let you style particular items according to their type, class, ID, attributes, or connections to other components. Depending on the degree of specificity needed, CSS selectors can be either simple or complex.
example
/* Element selector */
p { color: blue; }
/* Class selector */
.highlight { background-color: yellow; }
/* ID selector */
#header { font-size: 24px; }
The CSS selector types in this example are p,.highlight, and #main-header.
what are pseudo-classes in CSS?
Keywords known as pseudo-classes define a particular state of an element. These enable styling according to an element’s state, position, or user interaction. :hover, :active, :first-child, and :nth-child() are some common examples. They offer strong methods for producing dynamically styled and interactive pieces.
Example
a:hover { color: red; }
li:first-child { font-weight: bold; }
Explain the difference between var, let and const
var: A variable that can be updated and re-declared, either globally-scoped or function-scoped.
Let: Block-scoped; Updates can be made, but the same variable cannot be declared within the same scope.
const: Block-scoped; once declared it cannot be re-declared or changed.
Example
var x = 1; // Function or globally scoped
let y = 2; // Block scoped
const z = 3; // Cannot be reassigned
What is the box model in CSS?
The CSS box model explains the way elements show up as boxes with content, padding, borders, and margins. The content is what contains text and images; padding is space between content and the border; the border surrounds the padding; and margin makes up the area outside of the border. The four primary parts of this are content, padding, border, and margin, all of which can affect how the total width and height are calculated through this box-sizing property.
What is the function of media queries in CSS?
Media queries allow responsive design by applying different styles of CSS depending on the width, height, and orientation of the device. They allow developers to design layouts that fit different screen sizes from desktop monitors to mobile phones. Making responsive and mobile-friendly websites requires this.
Example
@media screen and (max-width: 600px) {
.column {
width: 100%;
}
}
What is the event loop in JavaScript?
The event loop is one of the core ideas that JavaScript uses to manage asynchronous processes. The callback queue is moved to the call stack when it is empty after it checks both the call stack and the callback queue continuously. With this technology, JavaScript can now handle asynchronous actions like setTimeout, promises, and others without halting the main thread.
Explain the difference between == and ===
- == (loose equality) performs type coercion before comparing, so the types must match.
- === (strict equality) checks for type and value, without converting of type.
Example
0 == false; // true
0 === false; // false
1 == "1"; // true
1 === "1"; // false
What is a JavaScript closure?
A closure is a function that, even after the outer function has returned, retains access to variables in its outer (enclosing) lexical scope. It sets up a way to save state in between function calls and allows for data privacy. Closures are a good way to implement advanced design patterns and create private variables.
Example
function createCounter() {
let count = 0;
return function() {
return ++count;
};
}
What is the purpose of the DOCTYPE declaration?
The DOCTYPE declaration makes sure that the page will render correctly and in standards mode by letting the browser know which version of HTML the page is using. It must be the first line of the HTML document. For HTML5, the simplest and most commonly used declaration is <!DOCTYPE html>.
Intermediate Level Questions
What do you mean by async and await?
The async/await syntax makes promises handled in code appear and behave like synchronous code. An async function always returns a promise, and await suspends execution until a promise is resolved. This makes actions based on promises easier to understand and code easier to understand as well.
Example
async function fetchData() {
try {
const response = await fetch('https://api.example.com/data');
const data = await response.json();
return data;
} catch (error) {
console.error('Error:', error);
}
}
What is the difference between display: block, display: inline and display: inline-block?
The display property in CSS decides how an element will display in a document.
display: block : The element takes up the full width of its container. The following element is moved to the next line when it starts a new line. regarding padding, margin, height and width.
It is used for structuring content like paragraphs, headers or containers and its examples include: <div>, <p>, <section>, <header>.
display: inline : Instead of beginning on a new line, the element respects the space of other inline elements by sitting next to them. Although margin and padding operate horizontally, you cannot explicitly define width or height as it will be ignored. Only the content’s width and height are considered.
It is used for styling text and other elements that appear inline within a line of text. And its examples include: pan, <a>, <strong>.
display: inline-block : Like inline, it can be placed next to other inline or inline-block elements and does not start on a new line. But , width, height, margin, and padding can be set, just like in inline.
It is used to make items (such as buttons or styled text blocks) that need custom dimensions but should behave like inline elements. And often used with <img>.
Visual comparison example
<div>
<!-- Block: Takes full width, new line -->
<div style="display: block; background: red;">Block Element</div>
<!-- Inline: Only takes necessary width -->
<span style="display: inline; background: blue;">Inline Element</span>
<!-- Inline-Block: Flows inline but respects sizing -->
<div style="display: inline-block; background: green;">Inline-Block Element</div>
</div>
What is the difference between map(), filter() and reduce()?
map(): creates a new array filled with the results of applying a given function to each element in an array.
filter(): generates a new array containing every element that passes a test implemented by the supplied function.
reduce(): reduces an array to a single value by using a function that builds up results.
Example
// map
const doubled = [1, 2, 3].map(x => x * 2); // [2, 4, 6]
// filter
const evenNumbers = [1, 2, 3, 4].filter(x => x % 2 === 0); // [2, 4]
// reduce
const sum = [1, 2, 3, 4].reduce((acc, curr) => acc + curr, 0); // 10
Describe CSS Flexbox.
With CSS Flexbox, the potent layout concept lets design flexibility and responsiveness while being an effective method of allocating space and aligning elements inside a container.
It introduces a flex container and flex items, which involve a container that is enabled to regulate the distribution, alignment, and arrangement of its child elements along a cross axis and a main axis, either vertical or horizontal.
Many layout issues that were hard to solve with standard CSS are solved with Flexbox, such as equal-height columns, vertical centring, and dynamic space distribution.
Example
.container {
display: flex;
justify-content: space-between;
align-items: center;
}
What are web components?
A collection of web platform APIs known as web components that allow you to design reusable, unique objects with unique functionality and aesthetics. Their three primary technologies are HTML Templates, Shadow DOM, and Custom Elements. This makes it possible to construct enclosed, modular websites.
Explain the concept of promises in JavaScript
Promises indicate whether an asynchronous operation will ultimately succeed or fail. Compared to callbacks, they offer a more streamlined method for managing asynchronous programming. There are three possible states for a promise: pending, fulfilled, or rejected. They enable asynchronous operations to be chained together.
Example
const fetchData = new Promise((resolve, reject) => {
// Asynchronous operation
if (/* operation successful */) {
resolve(data);
} else {
reject(error);
}
});
What is the difference between IocalStorage and SessionStorage?
The difference between local storage and session storage lies in how data is stored and retained in a web browser:
IocalStorage: In IocalStorage, data is stored locally with no expiration date. Even after closing and reopening the browser, data remains. and It is shared between the same browser’s tabs and windows (within the same origin). It is ideal for storing information that must be accessible for a longer amount of time, such as themes or user preferences.
SessionStorage: In SessionStorage Data is stored for a single session. If a tab is closed, data is deleted immediately. and even though they are from the same browser and origin, it’s tab-specific and not shared across tabs or windows. and Good for short-term data, such as form inputs or information from a single session.
Describe CSS Grid.
With CSS Grid, developers can easily construct complex, responsive web layouts thanks to its robust two-dimensional layout framework.
It offers vast positioning and sizing options for elements, along with characteristics that let you make adaptable, responsive designs that change automatically to fit various screen sizes and kinds of content.
The grid system gives developers almost complete control over the appearance of web pages through standardized layout techniques that are becoming easier to do than doing previously difficult tasks. It allows for powerful and easy elements in terms of placement and size.
Example
.grid-container {
display: grid;
grid-template-columns: repeat(3, 1fr);
gap: 20px;
}
What are generators in JavaScript?
Generators are pause-and-resume routines that gradually return a variety of values. They use the yield keyword and the function* syntax. By creating a single function that is capable of maintaining its own state, generators offer a means of defining an iterative algorithm.
Example
function* countGenerator() {
yield 1;
yield 2;
yield 3;
}
Explain the this keyword in JavaScript
The JavaScript keyword this indicates the context in which a function is run. Depending on how a function is invoked, its value changes. In arrow functions, it lexically captures the this value from the surrounding code; in global context, it refers to the global object; and in method calls, it refers to the object.
Advanced Level Questions
What is a JavaScript proxy?
A proxy in JavaScript is an object that encapsulates another object and catches its actions, such as assignment, deletion, function calls, and property access. In doing so, it allows developers to change the behavior of the target object. The new Proxy() constructor takes a target object and a handler object with traps (intercepting functions) and returns a Proxy. Proxies are helpful in data binding, validation, logging, and the implementation of dynamic behavior in objects. For example, a proxy may be used to block access to or modification of certain characteristics.
Example
const handler = {
get: function(target, prop) {
console.log(`Accessing property ${prop}`);
return target[prop];
}
};
const proxy = new Proxy({}, handler);
Explain the difference between Inheritance and composition
Composition and inheritance are two ways of structuring and organizing code in object-oriented programming.
Inheritance is a parent-child relationship between classes where child classes inherit properties and methods from the parent class. This method uses a hierarchical approach, which in certain instances, gives rise to tight coupling and rigidity.
Composition, on the other hand, is the composition of objects from other objects as building blocks, which promotes loose coupling and modularity. The style is centered on “has-a” relationships, such as “a car has an engine,” not “is-a” relationships. Modern programming tends to favor this composition because it is quite flexible and promotes better reuse and easier maintenance than with deep inheritance hierarchies.
What is the difference between server-side rendering (SSR) and client-side rendering (CSR)?
Server-Side Rendering (SSR) and Client-Side Rendering (CSR) are two Web page rendering techniques.
SSR generates HTML on the server and sends it directly to the client, providing faster initial page loads while also enhancing SEO because their content is visible to search engines right away. Round-trip interactions with the server could cause slower interactions afterwards and higher server stress.
While, CSR leverages JavaScript to render the content in the browser. After loading, it ensures smooth transitions and more interactive experiences but relies highly on the client resources. Though it reduces server load, the use of CSR can make initial page loads slow along with SEO issues if the same is not supported with strategies like pre-rendering or hydration.
What are WebSockets?
WebSockets are a full-duplex channel of communication via a single TCP connection between a client, often a web browser, and a server. WebSockets provide persistent and bi-directional data flow, which is different from HTTP, which is request-response orientated. This makes them perfect for real-time applications such as chat apps, gaming, and live updates.
Once the connection is established, there is a lesser overhead and latency as the client and server may transmit and receive data without constantly opening and closing connections. WebSockets rely on event-driven APIs to facilitate smooth communication and use the ws:// or wss:// protocol.
Example
const socket = new WebSocket('wss://example.com/socket');
socket.onmessage = (event) => {
console.log('Received:', event.data);
};
What are web Workers?
Web workers are JavaScript scripts that run outside the main thread of an application in the background, independent of the user interface. They allow for executing computationally expensive operations or tasks, such as huge datasets processing or complex computations without interfering with the user interface.
They can only communicate with the main thread by message because they run in separate threads and cannot modify the DOM directly. Web workers, for resource-intensive web applications particularly, improve performance and guarantee seamless user experiences.
Explain module bundlers (Webpack, Rollup, Parcel)
webpack, rollup, and Parcel are some of the other module bundlers that work on optimizing and managing java script modules and their dependence to use in online web applications.
Webpack: the highly customizable bundler is preferred for modular web development in application, it supports sophisticated functions such as loaders, plugins, and code splitting in bundles.
Rollup: focuses on more manageable bundles well-suited for libraries and projects requiring efficient tree-shaking.
Parcel: zero configuration bundler that supports almost all file types and is pretty fast to set up.
All these tools improve performance, streamline project management, and condense scripts into fewer files.
What are progressive Web Apps?
Progressive Web Apps (PWAs) are web applications which provide an app-like experience on any device by making use of modern web technology. Through offering capabilities such as offline access, push notifications, and fast load times, they combine the best features of mobile apps with the web.
PWAs don’t need app stores since they can be installed from a browser on a user’s device. PWA ensures seamless performance, even on uncertain networks, thanks to the basis in service workers, a manifest file, and responsive design principles.
Explain the virtual DOM
A virtual representation of the actual DOM with some very nice and thin performance benefits, by its light in-memory nature; React along other such libraries take advantage of this approach and enable applications to render faster with virtual updates before the real, but it only applies what was actually changed to real DOM to avoid overhead brought when using real DOM directly, further improving and increasing UI update speed efficiency as less reflows repaint are produced.
What are JavaScript decorators?
Decorators can be used to change classes, methods, or properties or add metadata. You can wrap or change the behavior of code at design time with their clear syntax for metaprogramming. It’s a JavaScript stage 3 proposal right now.
Example
function log(target, name, descriptor) {
const original = descriptor.value;
descriptor.value = function(...args) {
console.log(`Calling ${name} with`, args);
return original.apply(this, args);
};
return descriptor;
}
Explain Micro-frontends
This architectural technique divides the front end into smaller, stand-alone components in order to create modern online applications.
Each module can be created, implemented, and managed independently by different teams, each of which represents a feature or functionality of the program. This strategy allows teams to work in parallel using their favourite technologies, frameworks, or tools, thereby making it easier to scale and adapt.
This architecture encourages code reuse and lessens the complexity of maintaining a monolithic frontend, which is perfect for large-scale systems with numerous teams or products. To prevent conflicts and provide a smooth user experience, shared resources like styles and APIs must be planned.
Salaries for Front-End Developers (As per Ambitionbox.com)
| Company | Avg. Salary | Salary Range | Experience Required |
|---|---|---|---|
| TCS | ₹5.6 Lakhs | ₹2 L/yr – ₹8.8 L/yr | 0 – 8 yrs |
| Cognizant | ₹5.9 Lakhs | ₹1.9 L/yr – ₹10.3 L/yr | 0 – 5 yrs |
| Infosys | ₹5.3 Lakhs | ₹2 L/yr – ₹10 L/yr | 1 – 5 yrs |
| Accenture | ₹6.8 Lakhs | ₹2.5 L/yr – ₹11.3 L/yr | 0 – 6 yrs |
| Wipro | ₹4.8 Lakhs | ₹1.9 L/yr – ₹9.8 L/yr | 0 – 5 yrs |
| Capgemini | ₹6.8 Lakhs | ₹2.3 L/yr – ₹12 L/yr | 1 – 6 yrs |
| Freelancer.com | ₹4 Lakhs | ₹0.8 L/yr – ₹8 L/yr | 0 – 4 yrs |
| IBM | ₹12.3 Lakhs | ₹5.7 L – ₹19.3 L/yr | 1 – 9 yrs |
Conclusion
As we have discussed these interview questions for front-end developers, it is quite clear that a mix of basic knowledge and advanced experience is required for success in modern web development.
You can use these 30 questions as a guide to prepare for the interview by identifying your strengths and places for improvement.
Remember that understanding the concept behind and being able to adequately phrase your thoughts is much more vital to acing an interview than merely memorizing responses.
