29 Front End Developer Interview Questions And Answers (2021)

Why would you need to know all the most common front-end developer interview questions and answer?

In today’s technology world, a front-end developer should be tech-savvy and proficient to translate client needs into creative and interactive web applications. Gaining these skills requires front-end development training. Today, many top companies are looking to hire for front-end developer positions so that these developers can help them build elegant, intuitive, responsive and interactive user interfaces that work well on various devices. But the problem is that most candidates get confused or are not sure what type of interview questions they have to prepare for a front-end development interview which will eventually help them get hired.

It is quite simple to discover various practice questions, but it is hard to choose the right ones amongst these options.

Knowing the right questions is crucial for anyone that wants to ace a front-end developer job interview.

Whether you are a beginner or an experienced candidate, check out the list of top front-end developer interview questions and answers below. This article will help you to get to know both the questions and be prepared, so you will succeed in your interview.


Front-End Developer Interview Questions and Answers

Let’s see what the important front-end developer interview questions one needs to prepare for.

1. What are the technical and additional skills that are needed to be a front-end developer?

A good front-end developer needs to have a working knowledge about:

  • HTML
  • CSS
  • jQuery
  • Javascript

Apart from the above mentioned technical skills, a front-end developer should have the below mentioned “good-to-have” skills:

  • Experience in any of the most popular Content Management Systems (CMS) like WordPress,  Drupal, and Joomla and even the more recent ones such as Ghost
  • Knowledge of cross-browser testing
  • Knowledge of cross-device testing
  • Knowledge about OOPS and PHP.
  • Basic knowledge of SEO & tools like Adobe Photoshop, and CSS3 and HTML5, and various Javascript technologies such as native script, Angular, which are used to present web-based information to end-users.

2. Explain how you would ensure that your web design is user-friendly and what steps would you take to achieve this?

A front-end developer needs to communicate often and work alongside UX (User Experience) designers to imagine and conceptualize a web page that designs a user-centric experience, testing the website with users to ensure optimal design and ensuring that the web page or site is optimized for mobile phone browsing.

3. Describe Coffee Script?

CoffeeScript is a little programming language that compiles into JavaScript. It is an attempt to use the best parts of Javascript in a simple way. It also helps developers to write JavaScript code better by presenting the user with a more consistent syntax and skirting the unusual nature of JavaScript language.

4. Explain what is the clear property in CSS?

The clear property specifies on which sides of an element floating elements are not allowed to float. It is used when you don’t want an element to wrap around another element, such as a float.

5. Describe when would you use the CSS float property?

Float is used when you need to want an element of your web page to be pushed to the right or left and make other elements display around it.

6. What is a callback function?

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.

7. How do you structure your source code to make it easy for use by your colleagues?

A front-end developer needs to use common standards and explain their use of code organization and comments. They need to explain how they use notes in their programming process to explain the steps they have taken, thus ensuring efficiency of understanding amongst collaborators.

8. Explain what is the difference between Class and Prototypal inheritance in Javascript?

Inheritance in JavaScript is different from most other programming languages. The object system in JavaScript is prototype based, not class based. Objects in JavaScript are just a collection of a name (key) and value pairs. When it comes to inheritance, JavaScript only has one construct: objects. Every object has a private property which contains a link to another object called its prototype.

9. Can you explain the difference between visibility:hidden; and display:none?

With Visibility:Hidden the object is not visible but uses up it’s original space. With Display:None; the object is hidden and takes up no space.

10. Explain what is the difference between a host object and a native object in Javascript?

Host Objects that are objects supplied by a particular environment. Native Objects are standard built-in objects defined by Javascript. 

11. What is the difference between XHTML and HTML?

HTML and XHTML are both markup languages in which web pages and sites are written. The main difference between the two is that HTML syntax is SGML based while XHTML syntax is XML based.

12. Explain how variables differ in CoffeeScript as compared to JavaScript?

In JavaScript, before using a variable, we need to declare and initialize it (assign value). Unlike JavaScript, while creating a variable in CoffeeScript, there is no need to declare it using the var keyword. We simply create a variable just by assigning a value to a literal as shown below.

13. Can you tell us what are the benefits of CoffeeScript over JavaScript?

  • Easily understandable − CoffeeScript is a shorthand form of JavaScript, its syntax is pretty simple compared to JavaScript. Using CoffeeScript, we can write clean, clear, and easily understandable codes.

  • Write less do more − For a huge code in JavaScript, we need comparatively very less number of lines of CoffeeScript.

  • Reliable − CoffeeScript is a safe and reliable programming language to write dynamic programs.

  • Readable and maintainable − CoffeeScript provides aliases for most of the operators which makes the code readable. It is also easy to maintain the programs written in CoffeeScript.

  • Class-based inheritance − JavaScript does not have classes. Instead of them, it provides powerful but confusing prototypes. Unlike JavaScript, we can create classes and inherit them in CoffeeScript. In addition to this, it also provides instance and static properties as well as mixins. It uses JavaScript's native prototype to create classes.

  • No var keyword − There is no need to use the var keyword to create a variable in CoffeeScript, thus we can avoid accidental or unwanted scope deceleration.

  • Avoids problematic symbols − There is no need to use the problematic semicolons and parenthesis in CoffeeScript. Instead of curly braces, we can use whitespaces to differentiate the block codes like functions, loops, etc.

  • Extensive library support − In CoffeeScript, we can use the libraries of JavaScript and vice versa. Therefore, we have access to a rich set of libraries while working with CoffeeScript. 

14. Explain what are the difference between a GET and POST request?

Both a GET and POST method are used to transfer data from client to server in the HTTP protocol. The main difference between the POST and GET method is that GET carries request parameters appended in the URL string while a POST carries request parameter in the message body which makes it a more secure way of transferring data from client to server in HTTP.

15. Can you tell us when would you utilize the CSS clear property?

The CSS clear property is used when you want an element on the left or right of ` floating element not to wrap around it.

16. Describe what is the difference between Null and Undefined?

n JavaScript, undefined means a variable has been declared but has not yet been assigned a value. null is an assignment value. It can be assigned to a variable as a representation of no value.

17. Explain the importance of the HTML DOCTYPE?

DOCTYPE is an instruction to the web browser about the version of the markup language the page is written in. The DOCTYPE declaration need to be the first thing in your HTML document, before the <html> tag. The Doctype declaration points to a Document Type Definition (DTD). The doctype provides markup language rules, so a browser can interpret the content correctly.

18. Explain the difference between cookies, session storage, and local storage?

Cookies allow applications to store data in a client’s browser. Session storage property allows applications to store data until the browser window is closed. Local storage property allows applications to store data without an expiration date.

19. Describe what is a Thread-Local object in Python Flask?

A thread-local object is an object that is stored in a dedicated structure, attached to the current thread id. Flask utilizes thread local objects internally so that user don’t have to pass objects around from function to function within a request to stay threadsafe. Thread local storage performs within the current thread. This approach is helpful, but it needs a valid request context for dependency injection or when attempting to reuse code which utilizes a value pegged to the request.

20. Explain the syntax and how to use a Function as A Class?

function functionName(name){
this.name = name;
// Creating an object
var variable_name = new functionName(“Collective”);
console.log(variable_name.name); //Collective

21. What is lazy loading?

Lazy loading (also called on-demand loading) is an optimization technique for online content, be it a website or a web app. Instead of loading the entire web page or images and rendering it to the user in one go as in bulk loading, the concept of lazy loading assists in loading only the required section and delays the remaining, until it is needed by the user (for example when the user scrolls to the required image).

22. Explain the difference between classes and IDs?

Classes and ID selectors, both are utilized as hooks for CSS styles. ID’s are commonly used to style elements that only appear once on a page, such as one instance of a navigational menu. Classes are utilized to style different elements in the same way, such as the presence of links, buttons, forms, text, etc. 

23. What is Event Delegation?

Event delegation is the process of using event propagation to handle events at a higher level in the DOM rather than the element on which the event originated. It enables you to avoid adding event listeners to particular nodes; instead, you can add a single event listener to a parent element. 

24. How can you increase page performance?

  • Clean up the HTML document
  • Reduce external HTTP requests and external scripts
  • Use compressed and smaller image
  • Defer JavaScript to the bottom of the page
  • Use latest versions of code such as PHP
  • Minify CSS, JavaScript, HTML
  • Use CDN and Caching
  • GZip or Brotli Compress content
  • Leverage browser caching 

25. What is Ajax?

AJAX (Asynchronous JavaScript and XML) allows applications to transport data to/from a server asynchronously without refreshing the page. This means that it is likely to update parts of a web page, without reloading the entire page. For instance, your new Gmail messages arrive and are marked as new even if you have not refreshed the web page. 

26. What is the difference between Block, Inline,  Inline-block, and Box-sizing?

  • Inline is the default. For example: An inline element is <span>.
  • Block shows as a block element, such as <div> or <p>.
  • Inline-block shows an element as an inline-level block container.
  • Box-sizing displays the browser sizing properties.

27. What is Event Bubbling?

Event bubbling is a type of event propagation where the event first triggers on the deepest target element. It causes all events in the child nodes to be automatically passed to their parent nodes. The advantage of this method is performance because the code only requires to traverse the DOM tree once.

28. Explain what is a Closure? 

closure is a combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). A closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.


29. Explain how you deal with browser-specific style incompatibility?

There are multiple ways to work around this. The simplest way to proceed would be to utilize a conditional statement in the head tag of your HTML. In this way, you can recognize the browser and load an external stylesheet.


These are some of the most important front-end developer interview questions and answers. T/hey will assist you with your preparation for a job interview in front-end development. If we have missed any other important front-end developer questions, let us know in the comments below.

About the Author
David Attard
Author: David AttardWebsite:https://www.linkedin.com/in/dattard/
David has been working in or around the online / digital industry for the last 18 years. He has vast experience in the software and web design industries using WordPress, Joomla and niches surrounding them. As a digital consultant, his focus is on helping businesses get a competitive advantage using a combination of their website and digital platforms available today.

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