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Top Answers to UI Developer Interview Questions


UI design and development is a widely popular field nowadays. With an increasing number of businesses turning digital, the need for good UI developers is also increasing. This blog on UI developer interview questions caters to beginners as well as experts. We have curated a list of the most frequently asked interview questions for UI developers. This will help you prepare for your next UI developer interview. Let us take a look at the top UI developer interview questions generally asked in interviews.

Q1. Who are UI Developers and what do they do?
Q2. How is the role of a UI Developer different from that of a UX Developer?
Q3. What is the difference between a UI Developer and a Front-end Developer?
Q4. What is the full form of HTML and what is it used for?
Q5. How do you optimize a website’s assets?
Q6. What are the crucial skills for a UI Developer?
Q7. What is the difference between HTML Elements and Tags?
Q8. What is CSS used for?
Q9. What is JavaScript? Explain some of its features
Q10. What does DOCTYPE mean?

The UI developer interview questions are divided into three categories:

1. Basic UI Developer Interview Questions

2. Intermediate UI Developer Interview Questions

3. Advanced UI Developer Interview Questions

Basic UI Developer Interview Questions

1. Who are UI Developers and what do they do?

UI developers are responsible for developing the user interface. It is their responsibility to make sure that the UI meets the expectations of the users. A well-designed UI will ensure effective interaction between the user and the product. This is achieved by clean and responsive design.

Simply put, UI developers make sure the UI is functional, appealing, and convenient.

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2. How is the role of a UI Developer different from that of a UX Developer?

There are a lot of similarities between the roles of a UI and UX developer. UI developers primarily focus on creating interactive and navigation elements that help users easily navigate across the product, while UX developers focus on improving the quality of a user’s interaction with the product.

UX focuses on the journey of the user in solving a problem, while UI focuses on how the product looks and functions.

Watch this UI/UX Designer Interview Questions & Answers:

3. What is the difference between a UI Developer and a Front-end Developer?

A front-end developer is responsible for creating a web interface on the client side. This is done by using CSS, HTML, JavaScript, and other technologies. Front-end developers work on whole pages and develop a website as a combination of these pages. It is their responsibility to ensure that the website functions properly along with all its elements.

A UI/UX developer also uses CSS, HTML, JavaScript, and other technologies. They majorly use HTML and CSS. They are responsible for the visual elements that constitute the finished product such as buttons, tooltips, etc. A UI developer has to make sure that all the elements on the website are user-friendly and look pleasing.

4. What is the full form of HTML and what is it used for?

The full form of HTML is HyperText Markup Language.

HTML is the most popular language for creating websites. It comes with a series of elements and helps explain the structure of a web page. HTML elements are responsible for telling the browser how to display the content.

5. How do you optimize a website’s assets?

We can optimize a website’s assets by file concatenation, CDN hosting, file compression, offloading assets, refining code, reorganizing, etc.

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6. What are the crucial skills for a UI Developer?

A UI developer should have a keen eye for detail in every aspect of user experience.  They should also have some programming skills in HTML, JavaScript, CSS, JSON, AJAX, Java, SQL database development, and jQuery.

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7. What is the difference between HTML elements and tags?

HTML elements tell the browser how to render text. These elements become tags when they are surrounded by angular brackets <>. Tags usually come in pairs and surround the text.

8. What is CSS used for?

CSS is used for defining styles for web pages. This includes colors, fonts, and layouts. CSS allows us to define variations and layouts for different screen sizes. It can also be used with XML-based markup languages, independent of HTML.

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9. What is JavaScript? Explain some of its features.

JavaScript is a lightweight interpreted programming language with object-oriented capabilities. With JavaScript, we can make static HTML pages interactive. JavaScript is most widely used for front-end development like AngularJS and ReactJS. It is also used in back-end development like Node.js, Next.js, NestJS, etc.

Some of the important JavaScript features are:

  • JavaScript is a lightweight interpreted programming language.
  • JavaScript was designed to make network-centric applications.
  • JavaScript integrates with Java and complements it.
  • JavaScript integrates with HTML and complements it.
  • JavaScript is a cross-platform and open programming language.

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10. What does DOCTYPE mean?

DOCTYPE informs the browser about the type of HTML used on a web page. Browsers use DOCTYPE to understand how to render a page. If DOCTYPE is not used or if the wrong DOCTYPE is used, the pages load in Quirks mode.

11. What are the advantages of JavaScript?

  • JavaScript’s server interaction is less. It is easier to validate user input before the page is sent off to the server.
  • JavaScript provides immediate feedback to visitors. Users do not need to wait for the page to reload to know if they forgot to enter something.
  • JavaScript enhances interactivity. Users can create interfaces that interact with the cursor or keyboard.

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12. Define Semantic HTML

Semantic HTML is a style of coding. The tags are used to represent what the text has to present. Tags for bold or italic are not used as they call formatting and have no structure or meaning. The proper way to implement these tags is to use them along with emphasizing the structure and meaning of the text.

13. What are HTML Tags?

HTML tags help define how a web browser is supposed to display and format the content. They consist of content, opening tag, and ending tag. Some tags are unclosed like <hr>, which is used for the horizontal rule, and <br>, which is used for the break line.

Web browsers use HTML tags to distinguish between HTML and simple content. HTML tags help create HTML documents and render their properties. Each tag has a different property, and we can use as many properties as the code requires.

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14. Describe a few advantages of CSS

  • With CSS, users have better control over the layout of the web page.
  • The CSS style files are made separately from the HTML structure, so the file size can be smaller.
  • Due to the smaller file size, the bandwidth is also reduced, which helps in the files loading faster.

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15. Is JavaScript a case-sensitive language?

Yes, JavaScript is a case-sensitive language. Case sensitive here implies that all function names, identifiers, and variables have to follow the right capitalization of letters at all times.

16. Differentiate between quirks mode and standards mode.

Quirks mode and standards mode are two types of rendering modes in web browsers. In quirks mode, usually, the older browser’s behavior is copied, while in the standards mode, the pages are rendered in tune with the HTML and CSS specifications.

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17. What is the syntax difference between a bulleted list and a numbered list?

A bulleted list will use the < ul > tag, which means unordered list. A numbered list, on the other hand, will use the < ol > tag, which means ordered list.

18. Explain the layout of HTML

HTML layout specifies how a web page will be arranged. There are various HTML5 elements that are used to define various parts of a web page:

  • <header>: This defines the header for a section or document
  • <nav>: This defines a container for navigation links
  • <section>: This defines a section in a document
  • <article>: This defines a self-contained, independent article
  • <aside>: This defines stuff that is aside from the content, for example, a sidebar
  • <footer>: This defines the footer of a document

Intermediate UI Developer Interview Questions

19. What is a responsive website?

A responsive website can fit in all screen sizes and all devices—laptops, tablets, and mobile phones.

CSS media queries are utilized to rearrange the elements and to hide or display the elements from the UI.

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20. What is the difference between a window and a document?

A window is a root-level element in any web page, while a document is the direct child of the window object.

The global variables are defined on the window object, and documents are one of the properties of the window object. Document property can be accessed through windows or a document.

21. Explain event bubbling and event capturing

The order of the events that happen on an element is known as event propagation.

As soon as an event is fired up, the element bubbles up the DOM tree. This basically means that the child node is called first and then the parent node. This is called event bubbling.

Even capturing is the opposite of event bubbling. Here, first, the parent node is called, and then the child node.

22. Give an example of how to create an object in JavaScript

Here is how we can create an object in JavaScript:

var example_object =
    name: “objA”,	
    age: 20
    height: 100

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23. Explain the difference among the inline, inline-block, and block elements of HTML

Inline Inline-block Block
Does not start on a new line Does not start on a new line Starts on a new line
Possible to add spaces to the right and the left on an inline element Cannot add spaces Fills the right and left horizontal spaces on the web page
Cannot add padding and margins Can add padding and margins on all sides Can add margins and padding to the page
Examples: .nav and .nav li Examples: span and strong Examples: div and p

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24. What is the difference among relative, absolute, static, and fixed?

These are different position properties.

  • Relative position means moving an element with respect to its current position.
  • Absolute position concerns the element’s or parent element’s current position.
  • Static position is the default position of the element.
  • Fixed position is an element’s fixed position according to the respective device screen. Fixed elements do not move while scrolling.

25. Describe web accessibility.

Web accessibility is meant to ensure that websites, technologies, and tools are created and designed in a way that they can be used by people with disabilities. WAI-ARIA helps people with disabilities to use the web and understand it, interact with it, and navigate it.

26. What are the differences between local storage, session storage, and cookies?

  • Local storage provides maximum storage with no expiration date.
  • Session storage stores data according to sessions. It works like local storage but the moment a user closes the tab or browser, the data is deleted.
  • Cookies store small data that has to be sent to the server. The data stored is less than 4 KB.

27. Explain JavaScript Hoisting

JavaScript lets us access variables after they have been declared. Sometimes, the variable is defined at the bottom of the script but it is called before the declaration. In these cases, JavaScript throws an error that the variable is undefined.

Hoisting is a JavaScript mechanism where assigned variables and declared functions are hoisted to the top of their scope before the code is executed. So, the function is moved to the top of its range regardless of the scope being local or global.

28. Point out the differences among XHTML, HTML4, and HTML5

HTML stands for HyperText Markup Language.

  • HTML4 is the oldest version of HTML that is still used today. It has a loose syntax where things like closing tags are optional. One does not have to close a paragraph with a tag in HTML4 either. The loose syntax helps developers easily adapt to HTML. While loose syntax helps amateur developers, it also poses a problem when one’s trying to achieve a specific result in the browser.
  • XHTML was introduced to deal with this specific problem. Majority of sites that are developed today use XHTML. XHTML stands for EXtensible Hypertext Markup Language. It is based on XML, a more generalized markup language. In XHTML, all opened tags have to be closed. There are also some restrictions on which tags can be nested inside each other.
  • HTML5 is the newer version of HTML. It is becoming increasingly popular every day. HTML5 comes with new functionalities that help in how we use the web today. Developers are able to do a lot of exciting new things with the help of HTML5.

29. What is the importance of semantic elements?

The following are some of the reasons why semantic elements are important:

  • Semantic elements enhance the readability of the code. If the code is easier to read, it makes the developer’s work easier.
  • Semantic elements make the code more accessible. Developers, search engines, and assistive technologies are better able to understand the content and context of a website if the semantic elements are utilized.
  • Semantic elements make the code more consistent.

Advanced UI Developer Interview Questions

30. How would you optimize a website’s assets?

A website’s assets can be optimized by the following methods:

  • File compression
  • File concatenation
  • CDN hosting
  • Offloading assets
  • Reorganizing
  • Refining code

31. How can you reduce the page load time?

You can reduce the page load time in the following ways:

  • Reducing image size
  • Removing unnecessary images
  • HTTP compression; placing CSS at the top and script references at the bottom or in external files
  • Reduce lookups
  • Minimize redirects
  • Caching

32. What is the difference among linking to an image, website, and email address?

Tags are used when linking to an image. The image has to be specified in quotes using the source attribute, src in the opening tag <>.

An anchor tag is used when linking to a website, and <href> attribute is used to specify the website link.

The anchor tag has the text to be hyperlinked, and if you are linking to an email address, the <href> specification will be “mailto:[email protected]”.

33. How do floats function?

A float can have one of four values, and it can push the element to the right or the left.

  • Inherited: The element inherits the parent element’s float value
  • None: The element has the default float value and it does not float
  • Left: The element floats to the left of the container
  • Right: The element floats to the right of the container

34. What are the important things to remember when designing or developing multilingual sites?

The following things should be kept in mind while designing or developing multilingual sites:

  • The default language has to be set using Unicode encoding.
  • The “lang” attribute should be used.
  • Be aware of the standard font sizes and text direction.
  • The particular language word length should be taken into account; it can affect the layout.

35. Name the plug-ins available in the Bootstrap jQuery plug-in library.

There are many plug-ins available in the Bootstrap jQuery plug-in library as mentioned below:

  • Affix
  • Alert
  • Button
  • Carousel
  • Collapse
  • Dropdown
  • Modal
  • Popover
  • Scrollspy
  • Tab
  • Tooltip

36. What is the difference between require() and include()?

If an error is thrown while executing a code, the include() command can be used, and a warning is raised, while the require() command can be used if a fatal error has been raised.

37. What is an AJAX request? When would you use it?

AJAX is short for asynchronous JavaScript and XML. AJAX is a client-side process that is written in JavaScript.

If one needs to get or post data from a remote server, they can use AJAX to do it without reloading the page.

38. What is the difference between normalize.css and reset.css?

Reset.css is used to remove all default styles in the browser such as margin, border, and padding.

Normalize.css is used to create a standard booklike layout in all browsers such as bold headings, margins between paragraphs, common font, etc. This normalizes the style across browsers.

39. How would you find specific objects in an array of objects using JavaScript?

We can use the “find” method for that:

let customers = [
  { id: 0, name: ‘riya’ },
  { id: 1, name: ‘john’ },
  { id: 2, name: ‘mary’  }
let customer = customers.find(cust => === ‘mary’ );
--> { id: 2, name: ‘mary’ }

40. How would you filter an array of objects based on conditions using JavaScript?

We can do that using the “filter” function:

let data = [
let filteredData = data.filter(path => path.includes(‘dirb’));
--> [  ‘files/dirb/filea’,  ‘files/dirb/fileb’  ]

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