Top 25+ Most Asked Front end Developer Interview Questions and Answers

1) What are the main technical and additional skills required to become a front-end developer?

A candidate must obtain the following technical and additional skills to become a front-end developer:

Must Required Skills:

HTML: HTML is an acronym that stands for HyperText Markup Language. It is a standard markup language used for creating web pages. It describes the structure of a web page and tells the browser how to display the content on the web page.
CSS: CSS is an acronym that stands for Cascading Style Sheets. It is used to display HTML elements on a screen, paper, or other media. It can also be used to control the layout of multiple web pages all at once.
JQuery: jQuery is a very fast, small, and feature-rich JavaScript library designed to simplify the HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.
JavaScript: JavaScript is a scripting or programming language. This is used to implement the complex features on web pages.

Additional Skills:

Apart from the above mentioned technical skills, a good front-end developer should have the following skills and knowledge:

It would be great if the candidate has the knowledge and experience of working in any of the Content Management Systems (CMS) like WordPress, Drupal, and Joomla.
He must know the OOPs concept and PHP.
Knowledge of cross-browser testing is a plus point.
It is good if he has some basic knowledge about SEO & tools like Dreamweaver and Flash, which present web-based information to end-users.

2) What are some most used Git Commands and functions?

Following is a list of some most used Git Commands and functions:

Git Config: This Git command configures the username and email address.
Git inits: This Git command is used to initialize a local Git repository.
Git Add: This Git command adds one or more files to the staging area.
Git Diff: This Git command is used to view the changes made to the file.
Git Commit: This Git command makes changes to the head but not to the remote repository.
Git reset: This Git command is used to undo local changes to the state of a Git repo.
Git Status: This Git command displays the state of the working directory and staging area.
Git Merge: This Git command merges a branch into an active branch.
Git Push: This Git command uploads content from the local repository to a remote repository.
Git Pull: This Git command is used to fetch and download content from a remote repository.

3) How can you make your web design user-friendly, and what steps would you use to make it?

A front-end developer must follow the steps given below to make their web design user-friendly:

The front-end developer should focus on the web site's UI (User Interface) and UX (User Experience).
Imagine and conceptualize a web page that generates a user-centric experience.
Test the website with users to ensure optimal design. It also assures that the web page is optimized for mobile phone viewing.

4) What do you understand by Version Control System?

A Version Control System (VCS) is a program that is used to record any changes to a file or set of data so that we can restore it to a previous version if needed. It ensures that everyone on the team is working on the most up-to-date file version.

5) What is Coffee Script? Describe in brief.

CoffeeScript is a lightweight programming language that compiles into JavaScript. It is used to exhibit the good parts of JavaScript simply. It also enables developers to write JavaScript code better by providing constant syntax.

6) What do you understand by a callback function?

A callback function is a function that is passed as an argument to another function and ensures that a function is not going to run before a task is completed. This function runs right after the task has been completed.

7) What do you understand by clear?

A clear is used when we don't need an element to wrap around another element, like float.

8) What are the benefits of using CoffeeScript over JavaScript?

Following are some key advantages of CoffeeScript over JavaScript:

CoffeeScript is a lightweight programming language that compiles into JavaScript.
CoffeeScript contains a lot of lightweight add-ons like Ruby string Interpolation and Python style list comprehension.
CoffeeScript facilitates developers to express their programs with a lot shorter code than JavaScript.
CoffeeScript makes the JavaScript code good and more readable.
It is easy to perform everyday tasks with CoffeeScript rather than JavaScript.

9) What are the key differences between XHTML and HTML?

HTML and XHTML, both are markup languages. Let's see the key differences between them:

HTML	XHTML
HTML is an acronym that stands for Hypertext Markup Language. It is the most widely used language over the internet.	XHTML is an acronym that stands for Extensible Hypertext Markup Language.
HTML is a language used to create web pages and link them from one to another.	XHTML is considered a part of the XML markup language. It contains the features of both XML and HTML.
Tim Berners-Lee developed HTML in 1991.	XHTML was developed by W3C, i.e., World Wide Web Consortium, and was released in 2000.
HTML is extended from SGML and follows the format of document file format.	XHTML is extended from XML and HTML and follows the markup language format.
In HTML, it is not necessary to write Doctype at the top.	In XHTML, you must write Doctype at the top of the file.
HTML is not strictly case-sensitive. It is not necessary to put all tags in lower or upper case.	XHTML is strictly case-sensitive. Here, you have to put every tag and attribute in lower case.
In HTML, it is not necessary to close the tags in the order they are opened.	In XHTML, you must close the tags in the order they are opened.
HTML is an older language for linking web pages on the internet.	In comparison, XHTML is called a better version of HTML.
In HTML, it is not necessary to mention quotes while using attributes. For example: <JavaTpoint>.	In XHTML, it is mandatory to mention quotes while using attributes. For example: <JavaTpoint="JTP">.
In HTML, filename extensions are used as ".html", and ".htm".	In XHTML, filename extensions are used as ".xhtml", ".xht", ".xml".

10) How are variables different in CoffeeScript than JavaScript?

In JavaScript, we have to add a semi-colon for variables at the end of it to execute the program. On the other hand, in CoffeeScript, it is not necessary to add a semi-colon at the end of the statement.

11) What do you understand by the CSS box model?

The CSS box model is a way to handle CSS layout. This term is used when we talk about the design and layout of th elements. Each element is composed of its content, padding, border, and margin.

In other words, we can say that the CSS box model is essentially a box that wraps around every HTML element.

12) What is the difference between Git Pull and Git Fetch commands?

Git pull and Git fetch are the Git commands used to make changes and retrieve data. Let's see the key differences between them:

Git fetch	Git pull
The Git Fetch command downloads only new data from a remote repository. The Git fetch command is more like checking to see if any changes are available.	The Git pull command pulls new data and integrates it with the current working files, updating the current HEAD branch with the latest modifications from the remote server.
The Git fetch command does not include any new information in your working files.	The Git pull command combines remote modifications with those made locally.

13) What do you know about CSS Selectors?

CSS selectors are used to selecting or finding the HTML elements you want to style and make changes in their style. CSS selectors can be divided into the following five categories:

Simple selectors: These CSS selectors select elements based on the name, id, class, etc.
Combinator selectors: These CSS selectors are used to select elements based on a specific relationship.
Pseudo-class selectors: These CSS selectors select elements based on a certain state.
Pseudo-elements selectors: These CSS selectors are used to select and style a part of an element.
Attribute selectors: These CSS selectors select elements based on an attribute or attribute value.

14) What is the key difference between Class and Prototype-based inheritance?

The most important difference between class-based and prototype-based inheritance is that a class defines a type that can be instantiated at runtime. On the other hand, a prototype is itself an object instance. In JavaScript, the object system is prototype-based, not class-based. That's why inheritance in JavaScript is different from other programming languages.

Objects are just a collection of name and value pairs in JavaScript. In JavaScript inheritance, there is only one construct, called object. Every object has private property linked to another object known as its prototype.

15) What is the key difference between Null and Undefined in JavaScript?

Many people think that Null and Undefined are the same in JavaScript, but they have many differences. In the following table, we have included the key differences between them:

Null	Undefined
A null is an object with no value.	Undefined is a type.
Null is an intentional absence of the value. It is one of the primitive values of JavaScript.	In Undefined, the value does not exist in the compiler. It is the global object.
typeof null; // "object"	typeof undefined; // "undefined"
Null is equal to undefined but not identical. null == undefined // true	null === undefined // false
A variable is defined as null when trying to convey that the variable is empty.	A variable is defined as undefined when we try to convey that the variable does not exist or is not available.
Null is also referred to as false. Example: null ? console.log("true") : console.log("false") // false	When a variable is not assigned a value, it is called Undefined. Example: var temp; if(temp === undefined) console.log("true"); else console.log("false");

16) What is the difference between Visibility:Hidden;and Display:None;?

The Visibility:Hidden; and Display:None; both are used in front-end development when we don't want to display things on the screen.

Visibility:Hidden; is used when you don't want to show the things in output. It is not visible but contains its original space.
Display:None; is also used to hide the things on the screen, but it doesn't take any space.

17) What is the importance of HTML DOCTYPE?

In HTML, the DOCTYPE declaration points to a Document Type Definition (DTD). It is used to instruct the web browser about what version of the markup language the page is written. The DOCTYPE declaration is written as the first thing in the HTML document, before the <html> tag. It is a set of markup language rules that makes the browser easily and correctly interpret the content written within.

18) What is the key difference between a host object and a native object?

Host Objects are the objects supplied by a particular environment. On the other hand, the Native Objects are the standard built-in objects provided by JavaScript.

19) What is a marquee in HTML?

In HTML, a marquee is a scrolling piece of text displayed on the webpage. According to the marquee settings, it is either scrolled horizontally across or vertically up or down your web page. The marquee effect is created by using HTML <marquee> tag, which automatically scrolls the text or images up, down, left, or right.

Note: The <marquee> tag is now deprecated in HTML5. You can use JavaScript and CSS to create such marquee effects on the new web pages.

20) What is the key difference between cookies, session storage, and local storage?

Difference between cookies, session storage, and local storage

Cookies: Cookies allow applications to store data in the client's browser. These are small files that often include unique identifiers that web servers send to browsers. When a browser requests a new page every time, these cookies can be sent back to the server.
Session storage: Session storage is a popular choice for storing data on a browser. The session storage property facilitates developers to save and retrieve different values. This property allows applications to store data until the window is closed.
Local storage: The local storage property allows developers to store data without expiration. The key difference between local storage and session storage is that the session storage only keeps data for a particular session, and the data is cleared once the user closes the browser window. On the other hand, the local storage property allows applications to store data without an end.

21) What do you understand by Semantic HTML? How does it work?

Semantic HTML is a type of coding that uses HTML markup to reinforce the semantics or meaning of the information in web pages and web applications rather than merely to define its presentation or look. Semantic HTML is processed by traditional web browsers and many other user agents. It is used to emphasize the content's semantics or meaning.

The tags are different in semantic HTML as compared to normal HTML. For example, the <b></b> tag is not used for bold statements in semantic HTML, and the <i></i> element is for italic. Instead, we use the <strong></strong> tags and <em></em> tags respectively.

22) What do you understand by Web Accessibility?

Web Accessibility is a way to design, develop, and code websites and web tools that people with disabilities can also use. It makes using the technology easy for certain people who have difficulties hearing or seeing. It ensures that the web is also usable by people with a wide range of disabilities.

23) What is the difference between Git Merge and Git Rebase?

Git merge, and Git rebase are both used to integrate changes from one branch into another. Git rebase moves a feature branch into a master while the Git merge adds a new commit, preserving the history.

According to the official Git manual, the Git Rebase "reapplies commits on top of another base branch". On the other hand, Git merge "joins two or more development histories together". In other words, we can see that the Git merge preserves history as it happened, while the Git rebase rewrites it.

For example, if you are working on a new feature in a dedicated branch, and another team member pushes new commits to the master branch, the Git merge will incorporate new commits into your feature branch. Every time you need to include modifications, you would require an extra merging commit. On the other hand, in Git rebase, you can rebase the feature branch into master instead of merging it. This includes all the new commits in the master branch and rewrites the project history by creating brand new commits for each one in the original branch.

24) What is functional programming in JavaScript?

In JavaScript, functional programming is a programming paradigm mainly designed to handle pure mathematical functions as it focuses on writing more compounded and pure functions. It is used in JavaScript as JavaScript is a multi-paradigm language. In JavaScript, we can easily mix a lot of different paradigms inside a simple piece of JavaScript code. We can use procedural, object-oriented, and functional programming paradigms simultaneously in JavaScript, which makes it more powerful.

25) What do you understand by lazy loading? What are the advantages and disadvantages of lazy loading?

Lazy loading is a design pattern and optimization technique used in computer programming to delay the initialization of an object until a required period. It is also known as on-demand loading. This optimization technique is used for online content like a website or a web app. It is used to enhance the performance of the web page. In this technique, instead of loading the entire web page and rendering it to the user in one go as in bulk loading, only the required section is loaded, and it delays the remaining part of the web page until the user requires it.

Advantages of Lazy loading

Lazy loading or on-demand loading enhances the performance of web pages by reducing time consumption and memory usage.
It optimizes the content delivery on the web page.
It loads only a fraction of the web page first, which is required. Thus, the time taken is less, and the loading of the rest of the part of the web page is delayed, which saves storage.
It enhances the user's experience as the requested content is delivered quickly.
It avoids unnecessary code execution.
It is cost-effective as it practices the optimal time and space resources usage.

Disadvantages of Lazy loading

The developers have to add some extra lines of code to the existing ones to implement lazy load. It can make the code a bit complicated.
Sometimes, lazy loading may affect the website's ranking on search engines because of improper indexing of the content, which is not loaded.

26) What is the syntax of using a function as a class?

Following is the syntax of using a function as a class:

function functionName(name) {
this.name = name;
}
// Creating an object
var variable_name= new functionName("JTP");
console.log(variable_name.name); //JTP

27) What is the difference between a tag and an attribute in HTML?

Tags and attributes are two concepts used in HTML. They work together but perform different functions. The main difference between an HTML tag and an HTML attribute is that an HTML tag is a way of representing an HTML element in the program. On the other hand, an HTML attribute describes the characteristics of an HTML element. For example, <a>, <href>, <button>, and <div> etc. are HTML tags and src, class, and id etc. are the example of HTML attributes.

See this example:

In the above example, the image source (src) and the alt text (alt) are attributes of the <img> tag.

Difference between HTML tags and HTML attributes

HTML Tags	HTML Attributes
HTML tags are generally the starting and ending parts of the HTML code.	HTML attributes are used to define the character of the HTML elements.
HTML tags define a way to represent and hold HTML elements in the program.	HTML attributes are generally used to provide additional styling to the element.
HTML tags begin with < symbol and end with > symbol.	HTML attributes are always placed in the opening tag of an element.
HTML tags are like keywords where every single tag has a unique meaning.	HTML attributes provide various additional properties to the existing HTML element.

28) What is CSS float?

CSS float is a property that is used to specify whether an element should float to the left, right, or not at all. It is used when we have to push our web page element left or right and make all other elements cover around it.

29) What is the difference between inline and block elements in HTML?

The HTML inline and block elements are important areas of front-end development. Let us see the differences between the inline and block elements in HTML:

Block Elements: Block elements are types of blocks that contain many elements in a line itself. They consider top and bottom margins and don't contain any other elements next to them. They consume the full width available and always start in a new line.

Examples of Block elements:

<h1>-<h6>: These elements include headings of different sizes ranging from 1 to 6. Here, the smaller the number, the bigger the heading size.
<div>: This element is used to make separate content divisions on the web page.
<li>: This block element includes list items of an ordered or unordered list.
<ul>: This block element is used to make an unordered list.
<ol>: This block element is used to make an ordered list.
<hr>: This block element is an empty tag used to separate content by horizontal lines.
<p>: This block element includes paragraphs of content in the webpage.
<table>: This block element includes the tables in the web page when it requires tabular data.

HTML 5 Semantic block elements:

<header>: This semantic block element includes all the main things of the webpage like navbar, logos, and heading of the webpage.
<nav>: This semantic block element helps navigate different sections by including different blocks of hyperlinks in the webpage.
<footer>: This semantic block element contains all information about the web page's authorization, contact, and copyright details.
<main>: This semantic block element is used to specify the main content of the webpage.
<section>: This semantic block element is used to specify separate different sections in the webpage.
<article>: This semantic block element includes different independent articles on the webpage.
<aside>: This semantic block element mentions details of the main content aside.

Inline Elements: Inline elements take up only enough width that is sufficient to them and allow other elements next to it inline. They do not have top and bottom margins as block elements have only the left and right and consider the padding.

Examples of Inline elements:

<a>: This inline element includes hyperlinks in the webpage.
<br>: This inline element mentions line breaks in the webpage where ever needed.
<script>: This inline element is used to include external and internal JavaScript codes.
<input>: This inline element accepts input from the users and is mainly used in forms.
<img>: This inline element includes different images in the webpage to add beauty to the webpage.
<span>: This inline element is an inline container that takes necessary space only.
<b>: This inline element is used in places where bold text is needed.
<label>: This inline element provides a usability improvement for mouse users, i.e., if a user clicks on the text within the <label> element, it toggles the control.