Front End Developer Interview Questions

ClickJacking is a security attack where the user is fooled to click on something while they assume they are clicking another thing. The attack mostly happens by the HTML frames. ClickJacking is also regarded as the user interface redressing. It lets the user think that they are utilising a normal UI in the web page, but in actuality, there is an unseen UI in control; you can think of it as the user interface being redressed. When users click on one thing, assuming it to be secure and safe, the hidden UI executes another action.

• Meta tags are passed as pairs of name/value.
• Meta tags can include data about encoding, document title, character description, etc,
• Meta tags fit inside the HTML page’s head tag.
• Meta tags are not displayed on the page but it is to be shown on the browser.

An open-source front-end JavaScript library, ReactJS is used primarily for building user interfaces, especially for one-page applications. Also, it is utilized for handling the view layer for web and mobile apps. React lets programmers build large web applications that can modify data, without the need to reload the page. The main objective of React is to be quick, scalable, and easy. It functions only on user interfaces in the application and corresponds to the view in the MVC template. It can be utilized with a combination of other JavaScript frameworks or libraries, like Angular JS in MVC.

 Listed below are some of the advantages of REST web services:

• The curve of learning is simple since it works on the HTTP protocol.
• No contract clears between server and client, so roughly coupled application.
• REST approaches can be effortlessly tested on the browser.
• It also backs multiple technologies for the transfer of, for instance, image, JSON, XML, text, etc.
• It is a lightweight protocol.

The primary responsibility of the rendering engine is to highlight the requested page on the browser’s screen. Rendering engines can show XML and HTML images and documents. If you’re utilising additional plugins, the engines can also exhibit various documents like PDF.

• Receives the requested document: The contents of the requested document is obtained by the rendering engine from HTML’s networking layer.
• Construct the DOM tree: Parsed the HTML to the parsed tree and then set up the DOM tree, making use of it.
• Construct the CSSOM: CSSOM stands for CSS Object Model. Post the construction of the DOM tree, it identifies a link tag in the head section, which references the external style.css CSS style sheet. So, it parsed the CSS file in CSSOM tree, something which the Browser can comprehend as the DOM tree.
• Construct the Render tree: Utilise the HTML DOM tree coupled with the styling data of the CSSOM tree to set up a render tree. Render tree is the graphical depiction of the HTML, with the corresponding CSS. This tree enables painting the contents in their right order. Every node in the Render Tree is regarded as a renderer. The Render tree looks like this:
• Layout: When the renderer is developed and incorporated into the tree, it does not have a size or position. Computing these values is defined as layout. We use the coordinates system to position the element, such as the position of the root renderer is 0,0. The layout continues recursively via a part of the entire renderer hierarchy, calculating geometric info for every renderer that needs it. Beginning the layout process implies allowing every node the exact coordinates where it should show up on the screen.
• Painting of the Render Tree: The renderer tree is traversed in this stage and the renderer’s paint() method is hailed to exhibit the content on the screen. For good UX, the rendering engine will aim to exhibit the contents on the screen as soon as possible. It will not stand by until all the HTML is parsed to develop and layout the render tree.

CSS splits the page into grids and utilizes those grids to handle the HTML content. Utilizing the Grids, CSS can stack and highlight various elements in different parts of the grids.

From most other programming languages, Inheritance in JavaScript is different. JavaScript's object system is prototype-based, not class-based. Objects in JavaScript are just a set of value pairs and a name (key). Talking about inheritance, JavaScript just has one construct: objects. Each object has a private property that includes a link to another object named its prototype.

An iterative design procedure, User-centred design lets the designers focus on the clients and their needs in every design process phase. The user-centered design calls for linking users in the design process via a variability of design and research techniques to make usable and highly accessible products. User-centered design demands that designers should utilize a combination of generative (such as brainstorming) and investigative (interviews and surveys) methods and instruments to create an understanding of user requirements.

Frontend developers utilize different web technologies to change coded data into user-friendly interfaces. Many among these are Cascading Style Sheets (CSS), JavaScript, HyperText Markup Language (HTML), etc. Mentioned below are brief explanations of these technologies that frontend developers must be acquainted with.

• HTML: HyperText Markup Language depicts the content on the page like buttons, links, headings, paragraphs, and lists. It is the building block of websites and is utilized to define and mark content, so a browser shows it correctly. For instance, on a blog post, an image can be seen as an <img> in HTML code, so browsers will understand that they have to display an image.
• CSS: CSS stands for Cascading Style Sheets and is accountable for the style of your web pages such as animations., colours, and layouts. CSS appears more like a group of instructions that gives structure and style to a webpage than a programming language. It enables programmers to control a web application or website's layout, formatting, and presentation. While HTML depicts elements on a page, CSS is accountable for how users see the content. For instance, it handles the border, alignment, size, of an image in a blog post.
• JavaScript: JavaScript is one of three main elements, in front-end web development, that is required to end up with a web page that can be rendered accurately. It is now challenging to visualize websites without JavaScript as it allows programmers to make the sites interactive. This programming language can transform website content on the basis of a user’s action. For instance, at the top of the page, when you click on the Menu button, it will display a dropdown list of options or when you click on a button, it will toggle back and forth between closing and opening the Menu. JavaScript is great at figuring out the kind of browser being utilised, and then rendering the page in such a way that it is not only compatible with that page, but that it works the way it is designed. Using plugins is made easier by JavaScript. When complicated dynamic interactions are required for a site, JavaScript can be implemented to design its framework instead of simply depending only on HTML.
• CSS Frameworks, Libraries, and Preprocessors: Once you understand the fundamentals of CSS, then you can begin to work with various libraries and frameworks. These tools were designed as a way to help hasten the development process. Frameworks like Tailwind CSS, and Bootstrap let you incorporate the catalogue of classes into your webpage. Hence, you end up with mobile-friendly and professional designs. There are ample choices on the market and you don't require to know them all. It's often useful to look at related jobs and check what technologies they're employing. Then you can concentrate on the most in-demand skills.
• Testing and Debugging skills: As you are creating your application, there will be mistakes in your code that require to be fixed. Debugging is the act of recognizing those bugs and resolving them. Another essential skill to know is debugging. Documenting tests for your code is a way to assure that your code is accomplishing what it is meant to do.
• Version control: The way of tracking and the modifications to the project's code is version control. Git is regarded as a popular software that is utilized to track your code. If your code gets messed up, you can utilize Git to go back to an earlier version of your code rather than manually rewriting everything. Learning Git also lets you cooperate with others on a team and make modifications to the same code base from various locations. It is advised that you should start to learn Git and use a service like GitHub to host your projects.

While creating a complicated front-end application with tons of non-code static possessions, for instance, CSS, fonts, images, etc, then, of course, you should make use of Webpack since it has a lot of amazing benefits.

If you have a small application that doesn't have a lot of static resources and you only have to create one file of JavaScript to help the customers, then Webpack should be more overhead than needed.

There are numerous things accountable for lowering page load time. Let us look at the three best ways to reduce its loading time:

• Image Optimization: It is always advised to scale your videos and pictures before uploading them to a page.
• Browser Cache: The utilization of cache will boost speed for pages that you have visited already.
• Optimize and compress content: Compressing the content of a website decreases the load time of a page to a great extent.
• StyleSheet Reference on Top: Setting stylesheet reference to the header of a doc allows your page to load quickly.

When an HTTP request is sent to the server by the user, the user browser also sends a chunk of additional information regarding the language preference as the Accept-Language header. Then the server reads the HTTP request with the Accept-Language header and sends the document version back along with the right language and declares the language attribute Lang in the HTML tag.

Example:

Generally, Data-* attributes of HTML are utilized to accumulate the custom data, which is private to the web application or page. This custom data is for personalizing the JavaScript of the user as per the user action on the web page.

These days, Data-*attributes are not advised to utilize as the user can change the attribute easily just by utilizing the browser inspect console.

Example:

• Write less do more − For a huge code in JavaScript, we require comparatively a very less number of lines of CoffeeScript.
• Easily understandable − The shorthand form of JavaScript is CoffeeScript, its syntax is quite simple as compared to JavaScript. Making use of CoffeeScript, we can document clean, clear, and easily discernible codes.
• Reliable − CoffeeScript is a secure and reliable programming language to create dynamic programs.
• Readable and maintainable − CoffeeScript offers aliases for most of the operators, making the code readable. Also maintaining the programs written in CoffeeScript is effortless.
• Class-based inheritance − JavaScript does not have classes, in place of them, it offers powerful but complicated prototypes. Unlike JavaScript, in CoffeeScript, we can make classes and inherit them. Additionally, it also provides instant and static properties along with mixins. It utilizes JavaScript's native prototype to construct classes.
• No var keyword − There is no requirement to utilize the var keyword to form a variable in CoffeeScript, hence we can evade accidental or undesirable scope deceleration.
• Avoids problematic symbols − There is no requirement to utilize the problematic parenthesis and semicolons in CoffeeScript. In place of curly braces, we can utilize whitespaces to distinguish the block codes such as functions, loops, etc.
• Extensive library support − In CoffeeScript, we can utilize the JavaScript libraries and vice versa. Thus, we have access to a myriad set of libraries while operating with CoffeeScript.

The ‘use strict’ statement sets a few restrictions in the script. Typically, it is utilized to facilitate the strict mode of the script, making sure there could be no loose coupling like undeclared variables.

• MySQL: It is a Relational Database Management System (RDBMS), which makes use of SQL as a standard language to handle its database. Like different relational database management systems, MySQL makes use of a table-like structure to stow data.
• MongoDB: MongoDB is a NoSQL database that utilizes the JSON-like structure to stow data elements. To modify and access data in MongoDB, the programmer ought to make use of the MongoDB Query Language (MQL).

Generally, the function name is defined when we define the function itself, in normal user-defined functions, but in the case of an anonymous function, the function name is not defined. Here we make use of an assignment operator and variable to stow the function as an object, then utilizing that variable, we will be capable to invoke the function itself.

Example:

CSS image sprites assist to render numerous images in a single line image. In a nutshell, the CSS sprites merge numerous photos into a single large image. If a web page comprises different images, then it would raise its loading time as for every image the browser has to send a distinct HTTP request, but with the help of sprites, we have a single image to request.

• We can make a distinctive stylesheet for various browsers making use of server-side rendering.
• Another method is utilizing a library such as Bootstrap, which already has the code to manage the browser-specific styling issue.
• Reset or Normalize CSS can also be utilized. Multiple 3rd party plugins equip libraries for browser styling issues.

• An extra tool for the preprocessor is required.
• Preprocessor files can not be performed directly on the browser.
• Slow re-compilation of the preprocessor.
• For the preprocessor, you ought to know extra tools, which improve the learning curve of CSS.

• The consumption of resources can be reduced by the pages by enhancing the server response.
• Utilize JavaScript and External CSS instead of internal or in-line.
• Utilize the framework to ensure the front-end becomes more responsive to different devices.
• Open-source libraries can be used to manage the browser-specific styling issue.
• Make use of progressive loading like Lazy Loading to enhance the rendering of heavy elements, like videos and images.
• Connect the style sheet in the header and script at the top of the HTML's body tag.
• Utilize browser storage to keep user-specific private data.

Attributes are an element of an HTML document while properties are a part of the Document Object Model (DOM).

Example: <input type="text" value="Tech">

Here, value and type are the attributes of HTML, but when the statement is read by the browser and parses this code it will make a DOM with different properties, like accept, autofocus, accessKey, baseURI, checked, childElementCount, align, alt, childNodes, children, classList, className, attributes, and clientHeight.

Example:

var data = document.querySelector(input);  // here we created a document object of input tag
console.log(input.getAttribute('value')); // tech  // getting the attribute value
console.log(input.value); // tech   // getting the property of the input object

 == denotes abstract equality operator, and it inspects if two values are equal or not apart from their data types. Automatically, it transforms the type of both the operands and compares them.

Example: 

1=='1';    //true
1==1;   // true

=== denotes identity equality operator, and it inspects the values of both the operands and their data type. The outcome of the operation will be true considering both the operands are equal and have the same data type, or else it returns false.

Example: 

1===1   //true
1==='1'   // false

srcset is utilized when we wish to generate several resolutions of the exact image on several devices. This improves the UI. The browser will display low resolution on low-end devices, and high resolution of an image on high-end devices.

Example:

<img srcset="picture_low.jpg 480w,
             picture_high.jpg 800w"
     sizes="(max-width: 600px) 480px,
            800px"
     src="picture_high.jpg"
     alt="Elva dressed as a fairy">

Additional Useful Resources

• Front End Developer Salary in India – For Freshers & Experienced
• Front-End Developer Resume Sample (PDF): Full Guide and Example
• Best Front End Frameworks
• Difference Between Frontend and Backend – Frontend Vs Backend
• ​​​​Software Developer Vs Software Engineer

IN a JSON method, stringify is used to transform a JavaScript object into a string. JSON is a common structure to receive and send data between the web server and the client, and when we wish to send data to the webserver, the object ought to be a string.

Example:

In its BOX model, CSS comprises 4 elements:

• Content – Displays the main content and the text of the web page.
• Padding – This area encircles the content.
• Border – The border is the padding's outer layer.
• Margin – Margin is the area outside the border.

Progressive rendering is a process that is utilized generally to boost the web page's rendering content process. Now the rendering process is utilized in modern web development to enhance the mobile data uses of the user, async HTML fragments, prioritizing visible content, and lazy loading of images.

When you're preparing for your Front-end developer interview, try to code most of your layout without taking a glance at the result till the end. If CSS, HTMLare the most important aspect of front-end development, then JavaScript tops the list of important skills to own. Organisations will spend a lot of time during your interview to test your understanding of Javascript.

• Freshers:  While interviewing for front-end developer jobs for freshers you can come across this question. The best answer would be, " I have just begun my career, and do not have practical achievements, but I wish to explore and experience my potential by giving the best services to the company. It will be my privilege to work with your organization."
• Experienced: The best answer would be, “You should hire me for the role of front-end developer owing to my proven ability to create effective front-end user interfaces in line with contemporary best practices. I have experience working with JavaScript, along with the React framework, to create front-end applications.”

The biggest challenges faced as a front-end developer are:

• Make sure each UI element like button, link navigation,  works as planned despite the user having JavaScript or cookies disabled.
• Make sure everything looks similar across all browsers.
• HTML tables.
• Debugging JavaScript code.

As per the payscale, freshes, front-end developer gets an average of ₹305,498 per annum. An intermediate developer's salary is ₹452,073 on average. A senior developer can earn an average of ₹806,231.

 Yes, a front-end developer is regarded as a good career choice. It is in demand by top-tier players like Deloitte, Amazon, HCL, etc. Furthermore, the annual pay for a front-end developer is lucrative. In a nutshell, it is an in-demand position, good pay, and new learning each day.

Front-end development is considered as the programming which concentrates on the visual elements of an app or website that a user will interact with. Back end development concentrates on the side of a website that the user can't see, meaning the server-side.

The languages best for front-end development are HyperText Markup Language (HTML), Cascading Style Sheets (CSS), JavaScript, React, Angular, Vue.