Best Practices

30 Common Front-End Developer Interview Questions

If you happen to possess the required skills of a frontend developer and you are looking to pursue a career in it, then this article on frontend interview questions is for you. Below, we will explore front end developer interview questions and answers that can help you get prepped for your next interview.

What Is Front-End Development?

Front-end development is the process of creating the interactive and visual parts of a website that users see and interact with on their browsers. Front-end development also refers to client-side development. Basically, front-end developers specialize in creating and implementing a website's user interface (UI) and user experience (UX) to ensure that it is not only functional but also aesthetically appealing and user-friendly. Front-end engineers work closely with designers to bring their vision to life. They also work with back-end developers to integrate the user interface with the underlying data and server systems. This integration between design and functionality makes front-end development an essential component of web development.

In recent years, the growing expansion of applications for smart devices and mobile, with users accessing apps from an increasing variety of devices with different screen sizes and interaction choices, has been the main trend in front-end development. As a result, front-end engineers need to be well-equipped to always create a consistent, high-quality user experience across all devices and use cases. After going over the basics, let's explore a variety of front end developer interview questions and answers, which we have divided into junior, mid-level, and senior positions. These will give you a better idea of what you should expect and how to get prepped.

Front-End Developer Interview Questions

Junior Front End Developer Interview Questions

Interviews can be exciting as well as terrifying for aspiring junior front-end engineers. Below, we have gathered a list of questions designed for entry-level positions to give you the confidence you need to start your career in that field.

What are the fundamental design elements?

Answer: Some of the basic elements of design include:

  1. Line - Lines are marks formed using different tools, such as pens and brushes, or they can be formed when two shapes intersect.
  2. Color - Color is the light reflected by objects, and it has three key properties: hue, value (lightness or darkness), and intensity (brightness or dullness).
  3. Texture - Texture includes a shape's surface features, which might include qualities like smoothness and softness, as well as hardness and gloss.
  4. Size - Size is the amount of space a shape takes up in relation to other shapes.
Which are the technical proficiencies needed by a front-end developer?

Answer: Some of the required technical skills include: 

  1. HTML: This is also known as Hypertext Markup Language. It forms the foundation of web development and offers the structure and content of web pages, defining elements like headings, paragraphs, images, links, and forms.
  2. CSS: This is also referred to as Cascading Style Sheets, and it is responsible for styling web pages, including layout, fonts, colors, and responsive design. It ensures that the website looks appealing and consistent across different devices.
  3. JQuery: jQuery is a robust JavaScript library known for its rapid speed and features. It also simplifies DOM manipulation, event handling, CSS animations, and Ajax.
  4. JavaScript: This is a programming language that adds interactivity to websites. It enables the implementation of complex features on web pages.
  5. Version control: This is essential for tracking code changes. Git is a renowned version control system that allows developers to revert code versions, saving time and effort in the event of an error.
  6. Testing and Debugging skills: This involves testing out applications you have created to find any mistakes in your code and resolve them. 

Some of the additional skills a junior front-end developer should possess include:

  1. Having a grasp of Object-Oriented Programming (OOP) principles and PHP.
  2. Should be familiar with and have practical experience with content management systems (CMS) like Drupal, Joomla, and WordPress. 
  3. Having Cross-browser testing knowledge. 
  4. An understanding of SEO best practices to guarantee that web apps are visible and search engine-friendly. 
What do you know about CSS Selectors?

Answer: CSS selectors are used to choose or locate the HTML elements you want to change and make style modifications to. These selectors can be divided into five categories:

  1. Simple selectors are used to select elements based on the name, ID, class, etc.
  2. Combinator selectors are used to select elements depending on a particular relationship.
  3. Pseudo-class selectors are used to select elements based on a certain state.
  4. Pseudo-elements selectors are used to select and style a part of an element.
  5. Attribute selectors are select elements based on an attribute or attribute value.
What is Semantic HTML? How does it work?

Answer: Semantic HTML is a form of coding that employs HTML markup to support the semantics or meaning of the content in web pages and online apps rather than only to define its presentation or look. It is used to draw attention to the content's semantics or meaning. It is employed to highlight the semantics or meaning of the content. In contrast to standard HTML, semantic HTML uses different tags. For instance, semantic HTML doesn't use the older i>/i> element for italics or the <b></b> tag for bold text; rather, it uses the <strong> and <em> tags instead.

Briefly describe three strategies to decrease page load time.

Answer: Multiple variables contribute to lowering page load time. Some of the three most effective methods for speeding up its loading include:

  1. Image Optimization: Always scale videos and images before uploading them to a page.
  2. Browser Cache: Using cache will increase the performance of sites that were previously visited.
  3. Optimize and compress content: Compressing a website's content reduces page load time.
What is React JS?

Answer: ReactJS is an open-source front-end JavaScript library used mainly for developing user interfaces, most especially for one-page applications. It is also used to manage the view layer for both mobile and web applications.

Software engineers use React to develop large web applications that can modify data without needing a page reload. Basically, React's primary goals are to be speedy, scalable, and easy to use. It can work with a number of different JavaScript frameworks and tools, such as AngularJS in MVC

What is ClickJacking?

ClickJacking is another term for user interface redressing. ClickJacking is a security attack where the unsuspecting user is tricked into clicking on something when they think they are clicking on something else. Usually, the HTML frames are the main vector for the attack. 

It gives the user the impression that they are using a standard UI on the website, but in reality, another UI is in charge; you could think of it as the UI being redesigned. Users click on anything, believing it to be safe and secure, but the disguised UI really performs another activity. 

For example, imagine a situation where a user is on a website that has a "Download" button for a file they want to download. Clickjacking is at work when the "Download" button is covered by an invisible "Like" button from a social media platform by an attacker. When the user clicks what looks to be the "Download" button, they unintentionally also click on the "Like" button on the attacker's preferred social network page, which might result in unwanted actions or consequences.

Mid Front End Developer Interview Questions

As your front-end development career progresses, no doubt, you are going to encounter a more complex number of questions. This section dives into mid-level questions that cover numerous topics.

In the context of web development, describe what lazy loading is.

Answer: Lazy loading is basically a performance optimization approach that delays the loading of unnecessary content, such as images or scripts, until it is needed. This enhances user experience by decreasing page load times and conserving bandwidth.

What does SOLID stand for, and what are its guiding principles?


  1. "S" stands for the Single-responsibility principle, advocating that a class should have a singular job. 
  2. "O" represents the Open-closed principle, highlighting that objects should allow for extensions without necessitating modifications to their core structure.
  3. "L" denotes the Liskov substitution principle, which states that if a property q(x) can be verified for objects of type T, it should also hold true for objects of type S, where S is a subtype of T.
  4. "I" stands for the Interface segregation principle, highlighting the importance of not imposing unnecessary interface requirements on clients.
  5. "D" signifies the Dependency Inversion Principle, which encourages entities to rely on abstractions rather than specific implementations.
What differentiates PUT and POST semantically?

Answer: PUT precisely and specifically places a file or resource at a given URI. If this URI already contains a file, PUT will replace it.

POST delivers data to a certain URI and then waits for that URI's files or resources to handle the request. The server now chooses what action to do with the data in relation to that resource.

What is your understanding of CSS image sprites and their use?

Answer: CSS image sprites make it possible to render several pictures in a single line image. Simply put, CSS sprites combine many images into one sizable image. A web page would take longer to load if it contained multiple images because the browser would need to send separate HTTP requests for each image. However, with the help of sprites, only one image needs to be requested, which will save bandwidth and reduce the number of server requests.

Give some suggestions about how to resolve the browser-specific styling issues.


  1. Once it has been determined which particular browser is the source of the issue, make separate stylesheets specifically for that browser. These stylesheets will load only when the targeted browser is being used. This method often calls for server-side rendering. 
  2. Use frameworks like Bootstrap, for example. This type of framework is designed to handle browser-specific styling issues.
  3. Use the Autoprefixer tool to add the required vendor prefixes to your code automatically. 
  4. Include a CSS reset or normalize stylesheet at the beginning of your project's CSS. These stylesheets help with establishing a uniform foundation for your styles, thereby minimizing inconsistencies and browser-specific issues.
What is webpack?

Answer: Webpack is a JavaScript module bundler that is open-source. Its primary function is to arrange all of the assets, including Javascript, pictures, fonts, and CSS, in a dependency graph. Webpack grants control over how it handles various assets it encounters.

What is a Grid System?

Answer: A grid system is an essential framework that allows software engineers to organize content vertically and horizontally in a structured layout. It is made up of two primary components: rows and columns. Grid systems are essential in web design because they give a consistent and orderly framework for arranging content. Some examples of grid systems include Simple Grid, Pure, Flexbox Grid, Bootstrap, and Foundation.

How can you organize your CSS and JavaScript such that other developers can work with it more easily?

Answer: Organize my stylesheets into parts for every part of the site. Each section contains comments throughout the code, which will allow other developers to modify it.

AngularJS vs. jQuery: When should you use each?

Answer: jQuery is ideal for simple DOM manipulations and lightweight and quick web page upgrades. In contrast, AngularJS is a more comprehensive framework with capabilities like data binding, routing, and a structured MVC architecture intended for creating complex web applications. Ultimately, the decision is based on the particular specifications and size of the project.

How does the front-end load balancer operate? What is load balancing?

Answer: Load balancing is a method for properly distributing workloads over several servers or server clusters, and a front-end load balancer plays an important role in this process. It makes use of a virtual IP address (VIP) as a single point of entry for client requests and intelligently directs those requests to the best back-end server based on factors like server health, the load at any given time, and scheduling algorithms. Examples of common scheduling methods are Round Robin, Least Connections, and Weighted Round Robin.

Senior Front End Developer Interview Questions

Below, we explore key senior frontend interview questions to help you ace your next interview.

How does progressive rendering work?

Answer: Progressive rendering is a technique that is frequently used to speed up the process of producing content on a web page. Modern web development now makes use of the rendering process to improve the user's mobile data usage, async HTML fragments, giving visible content priority, and lazy loading of images.

When should you choose React or Vue?

Answer: React or Vue would be suitable options for small projects when the application is simple and doesn't need a lot of complicated features. Both frameworks are excellent for small projects because they are lightweight and simple to use.

How do you choose between Angular or React, depending on the scope of the project?

Angular or React will be a better option for medium-sized projects if the application needs more advanced capabilities. Larger, more complicated projects benefit greatly from comprehensive frameworks like Angular, which has numerous built-in features. On the other hand, software developers can use React to build complex apps by interacting with other libraries and technologies, 

Angular is frequently the first choice for large-scale enterprise projects when the application is highly complex and needs a lot of features. Generally, large-scale applications benefit greatly from Angular's robust architecture and broad built-in features. In addition, Angular supports TypeScript, a potent programming language that can help guarantee code quality and maintainability in large projects.

Suggest how you can optimize our front-end page.


  1. Server Response Optimization: Improve server response speed by streamlining back-end operations, employing caching techniques, and reducing needless server requests. This can swiftly increase the loading time of a page.
  2. External JavaScript and CSS: Create distinct external files for your JavaScript and CSS rather than using inline or internal styles. This improves browser cache and speeds up page load time.
  3. Responsive Frameworks: Make use of frameworks for responsive web design, such as Foundation or Bootstrap. Because these frameworks include pre-built elements and responsive layouts, your front-end will be mobile-friendly and adjustable to various devices and screen sizes.
  4. Open-Source Libraries: In order to handle browser-specific styling difficulties, use open-source modules and frameworks. Libraries like Modernizr and Autoprefixer can be used to guarantee cross-browser compatibility,
  5. Lazy Loading: For large items like images and videos, use progressive loading approaches like lazy loading. This improves initial page load times by delaying the loading of unnecessary content.
Explain the Prototype Design Pattern

Answer: The Prototype Design Pattern is a creational pattern focusing on making new objects but doing so in a unique manner. It involves using a prototype or sample object to initialize the new objects with pre-defined values or properties rather than creating brand-new instances from scratch. For example, initializing business objects with values that match the default database values is a typical use of this pattern. Although the Prototype pattern may not be widely used in classical languages, JavaScript, which is a prototypal language, naturally makes use of this pattern when creating new objects and the prototypes that go with them. It's a powerful concept that makes object creation efficient and can make working with complicated data structures in JavaScript easier.

Briefly discuss the drawbacks of using a CSS Preprocessor such as Sass.

Answer: There are several drawbacks to be aware of, even if CSS preprocessors like Sass have many benefits, like maintainability and code modularity. These drawbacks include:

  1. First off, compiling the preprocessor code into normal CSS requires an additional tool or build step, which can complicate your development workflow. 
  2. The inability to directly execute preprocessor files in the browser makes debugging more difficult. 
  3. The re-compilation procedure can take longer, particularly for bigger applications.
  4. Also, knowing a preprocessor's specialized syntax and functionality is necessary for using it, which may make learning CSS development more difficult.
How do you define content security policy?

Answer: An HTTP header called Content Security Policy (CSP) enables website operators to keep an eye on and manage where resources can be loaded on their site. One of the best ways to guard against cross-site scripting (XSS) vulnerabilities is by using this header. All new websites must have CSPs, and it is strongly advised to implement CSPs on all high-risk websites already in existence because it is impossible to retrofit CSPs on all current websites.

The option to disable unsafe-inline JavaScript, which helps fight XSS attacks by blocking the execution of potentially dangerous inline code created from user inputs, is one of CSP's main advantages.

The "use strict" statement is used for what?

Answer: The 'use strict' statement imposes some limitations on the script. In general, it is used to support the script's strict mode, ensuring that there are no loose couplings like undeclared variables.

Why do we need the W3C Standard Code?

Answer: One of the primary objectives of such standards is to ensure cross-platform interoperability and smaller file sizes. By using CSS, these standards aim to separate "content" from "formatting". Ultimately, it makes development and maintenance easier.

What components are in Angular?

Answer: Every program has different components. Each component serves as a logical boundary of the application's functionality. It is a class that contains the data, logic, and methods for a view. The following is an overview of the components:

  1. Class: This is similar to a C or Java class, which has properties and methods.
  2. Metadata: This is used to enhance and expand the class's functionality.
  3. Template: This serves to define the HTML view that the application displays.
Give an example of the front-end development task lifecycle.

Answer: The stages of a task's life cycle in front end development can vary based on the project management methodology being used, but they often occur in this order: 

  1. Requirement gathering: Gathering requirements from the client or stakeholders is the first step in the task. This involves being aware of the features and functionalities that must be deployed on the front end.
  2. Planning: Planning comes next after acquiring the necessary information needed. This is dividing the task into smaller subtasks, figuring out how long each one will take, and choosing the sequence in which to complete them.
  3. Design: At this step, the front end's design gets created. Wireframes, mockups, and prototypes must all be produced in this process. 
  4. Development: As soon as the design is complete, front end developers go to work on the actual front end development. JavaScript, CSS, and HTML are all used in the coding for this. In order to speed up the development process, developers may leverage frameworks like React or Angular. 
  5. Tests: After development is complete, the front end is tested to make sure it complies with specifications and performs as intended. Usability, compatibility, and performance testing are all part of this process.
  6. Deployment: Following testing and approval, the front end is put on a server or hosting platform. This involves getting the required infrastructure in place, setting up the server, and uploading the front end files.
  7. Maintenance: Maintenance is essential in order to ensure the front end keeps working properly after deployment. Hence, required updates, new features, and bug fixes must be made.

Most importantly, to guarantee that the project is effectively completed, communication between the development team, the client, and other stakeholders is of the utmost importance throughout the whole life cycle of the project.

React is a library, while Angular is a framework. What distinguishes a framework from a library?

from a library?

Answer: A framework is a wider range of tools and practices that provide a framework for developing a full application. A framework often consists of a collection of tools and libraries as well as guidelines and best practices for the development process. In order to make sure that their code fits well with the rest of the program, software developers frequently strictly follow the framework's rules, which offer a more prescriptive approach to application development.

On the other hand, A library is a collection of pre-written programs that may be used to carry out particular tasks, including building user interfaces or managing network requests. In order to complete a specific task, the developer's code can often call a collection of functions or classes that are provided by a library. Libraries are made to be adaptable and can be used in many different applications.

Although both libraries and frameworks offer pre-written code that can be used to create applications, the fundamental difference between the two is in the scope and degree of abstraction. In contrast to frameworks, which offer a more complete set of tools and rules for creating complete programs, libraries are more adaptable and can be used for a range of tasks.

How should third-party APIs be integrated into front-end applications?

Answer: Developers need to follow several vital steps in order to integrate third-party APIs into a front-end application. These include:

  1. Identify the APIs you want to integrate: The first step involves figuring out which APIs you want to use. It also encompasses gaining an understanding of their capabilities, limitations, and requirements. It's essential to carefully read the API documentation to fully understand the parameters, data types, and authentication requirements.
  2. Choose the integration technique: Based on the API, you might have to decide between client-side and server-side integration. When integrating with a payment gateway, for instance, handling API requests on the server side is often safer and more secure than revealing sensitive payment information on the client side.
  3. Create API requests: Send HTTP queries to the API endpoint to initiate communication with the API. Fetch API or the Axios library are a couple of technologies that may be used for this. Authentication tokens or data to be submitted to the API are examples of the necessary parameters you must include in the request.
  4. Process API responses: The API will respond with data after you send your request. Based on the data format the API sends back, you will need to handle the response correctly. You could parse the response data and show it in your app, or you could use it to make more API requests.
  5. Handle errors: In your front-end app, it's important to handle API errors well. This includes managing HTTP status codes and displaying the right error messages to the user.
  6. Test and debug: Finally, make sure your API integration works the way you want it to by testing it carefully. Test your API requests with tools like Postman to make sure you are getting the expected responses. Debug any issues that develop in your code, and ensure you handle any edge cases or error possibilities.

In conclusion, a front-end developer should possess a wide range of skills, including knowledge of JavaScript, HTML, CSS, and vital ideas like responsive design, web accessibility, and SEO. This guide has explored a wide range of front end developer interview questions and answers, offering detailed answers to help you prepare and excel in your next interview. At YouDigital, we are a European boutique software company that specializes in offering a comprehensive range of services in software development outsourcing. This unique expertise allows us to source and provide top-tier senior remote developers who excel not only in their technical abilities but also in their communication skills. Get in touch with us today for all your software development needs. Remember to check out our other posts that cover other in-depth subjects like Python and Javascript, amongst others.

Share article

Check other articles
Why You Should Hire a Web Development Company

Why You Should Hire a Web Development Company

Benefits of prioritizing a web development company to aid your business - particularly startups searching for tangible market shareholdings.

Why Product Validation is Important for Your Business

Why Product Validation is Important for Your Business

Risk is undoubtedly a crucial part of any business. You might need to undertake some risks to get ahead of the competition. Most companies have an

Why Companies Prefer to Develop Software in Poland than in other  Eastern European countries

Why Companies Prefer to Develop Software in Poland than in other  Eastern European countries

As businesses seek to expand their operations, the need to scale software development, develop software in Poland and cut costs will become even more prominent.