Front End Developer Interview Questions And Answers 2023

Website’s assets resources are images, styles, scripts, and also external media.

To optimize these assets you can opt following ways-

• Make all assets lightweight so that it's easy to download
• The use of a Content Delivery Network (CDN) helps to optimize assets
• While hosting assets on different domains make sure to reduce DNS lookups.
• Use of CSS Sprites.
• Disable etags.

Skillset required from a Front end Developer listed below:

Technical frontend developer skills

• HTML and HTML5
• JavaScript and JQuery
• Responsive Design
• Testing
• Creativity
• Version Control Systems and other developer tools
• CSS3

Apart from the above mentioned technical skills also should have knowledge of cross browser testing, OOPS, CMS or any Framework and basic knowledge about SEO and tools.

CORS is Cross-Origin Resource Sharing and it allows you to make requests from one website to another website. But for security reasons, a browser is not allowed to load requests to other domains when those requests are generated by scripts. CORS addresses this issue by supplying a header that will define which domains can make XMLHttpRequests.

• Minimize External HTTP Requests
• Minify JS, CSS and HTML
• Optimize JS and CSS Performance
• Use CDN and Caching to increase Speed
• Compress Images and Files
• Prefetch should be Enable

It is a small language that compiles into JavaScript. In this programs is written with less code and in more human readable forms.

The golden rule of CoffeeScript “It is just JavaScript”

• It was developed by Jeremy Ashkenas in year 2009.
• It is used because of CoffeeScript code is shorter and converts seamlessly to JS. It helps developer in writing an simple and easily readable code.
• It is something which makes JS easier and effectively reducing our code to one third. It compiles into JS on execution which is Inspired by Python and Ruby.

There are many things responsible for reducing page load time. We will tell you the best three ways to reduce it’s loading time-

• Image Optimization: Always scale your pics or videos before uploading them to a page.
• Browser Cache: The use of cache will increase speed for pages that you have already visited.
• Compress and Optimize Content: Compressing the content of a website reduces page load time to a great extent.
• StyleSheet Reference on Top: Putting stylesheet reference to the header of a document helps your page to load faster

It can be assigned to a variable and has no value in case of null but on the other hand undefined means a variable has been declared but has not yet been assigned a value.

var x = 840;
x.toString().length;

A callback function is a function which is accessible by another function and invoked after the first function if that first function completed.

• Box Shadow: It adds a shadow to an element.
• Opacity: This property of CSS3 makes elements completely transparent.
• Rounded Corners: Earlier for rounded corner developers had to write long codes but these features solved that problem.
• Attribute Selectors: Now developers can select HTML elements according to the attributes instead of applying IDs or classes.
• CSS Colors

It is a function that was declared without any function named identifier to refer to it. It is usually not accessible after its initial creation. These functions are created at run time.

Normal funtion

function helloFunction() {
    alert("Hello this is bestinterviewquestion.com");
}

Anonymous function

var helloFunction = function()
{
    alert("Hello this is bestinterviewquestion.com");
}
helloFunction();

Ajax stands for Asynchronous JavaScript And XML and it is not a programming language. It uses XML to transport data, but it is equally common to transport data as JSON text or plain text.

Responsive Web Design : It built on a fluid grid that will change with the browser automatically, no matter what the screen resolution is holding content can break apart and realign if need be.

Adaptive Web Design : It not necessarily set on a fluid grid; targets specific device resolutions like (320, 768, 1024 etc); can have set relative widths with (%) and controlled by media query.

To check if a variable is a number, we can use isNaN() function in JavaScript. It determines whether a value is not a number.

Flash of Unstyled Content is also called Flash of unstyled text. It is an occurrence where a web page appears shortly with the browser’s default styles. The web page corrects or sets itself as soon as the style rules are loaded and applied.

Event Bubbling

In an event, bubbling handlers are called when one element is nested into a second element, and both the elements have a listener for the same event. E.g. A click. Nowadays all modern browsers have event bubbling by default.

Event Capturing

Event capturing starts from the top element to the target element. Modern browsers don't support this event but we can achieve that with the help of code.

It is called ternary expression because of the ternary operator (?:). Word Ternary indicates “three” means it takes 3 arguments and is one-lined shorthand for an if-then statement.

With the help of “Strict Mode,” users can write secure Javascripts easily. It changes bad syntax into real errors. It can be declared by placing “use strict”; at the beginning of a function or script.

Advantages

• It eliminates some JavaScript errors by changing them to throw errors.
• Strict Mode prevents errors when some unsafe actions are taken.

Disadvantages

• If a library that was in strict mode but by mistake used in normal mode then that might call some actions and wouldn’t work as expected.
• One of the major disadvantages of using this mode is error might fail silently.

A promise means to the object which is responsible for producing a single value as the result in the upcoming future whether it is resolved or not.

Promises are used to manage asynchronous operations.

How to use the promise:

Let promise = new Promise(function(resolve, reject) {
// asynchronous call
});
Promise uses a callback function as the argument and that callback function takes 2 arguments: the first one is the resolve function or the other one is the reject function.

NOTE: Normalizing is way much better than Resetting as there is no point in resetting all elements and styling them again.

CDN is a Content Delivery Network and is a series of servers that are distributed all over the world and all are linked together.

Benefits Of Using CDN

• CDN files are placed on different domains. Apart from that, a single Content Delivery Network allows the browser to download four files at a single time.
• It boosts performance and saves money.
• It decreases the load on the server.
• CDN increases the number of concurrent users.

Domain prefetching is a process of resolving a website’s IP address before a user clicks on it.

Types of prefetching

• Link Prefetching
• DNS Prefetching
• Prerendering

This process allows the browser to perform the DNS lookups on a page in the background and at the same time the user can browse the current page. This minimizes latency as when the user clicks on the links they don't have to wait for DNS lookup.

Every HTML document consists of the following building blocks-

• Attribute: In HTML an attribute provides extra information about an element and that is applied within Start TAG. It contains two fields i.e. Name and Value
• Tags: Tags in HTML surround the content and add meaning to it and they are written between < and > brackets.
• Elements: In HTML file, everything written within tags are termed as HTML elements.

This method is used to converts JavaScript objects into strings. When sending data to a web server the data should be like string.

Three.js having various features that are given below:

• Effects and Animations
• Scenes and Cameras
• Data loaders and Shaders
• Geometry and Objects
• Debugging and Virtual reality
• Utilities and Materials
• Support etc

• tables were used for tabular data and not for layout.
• tableless layout make a nicer appearance.
• <div> require less actual code than tables.
• We can get better performance with separated out css files because then the browser can cache the presentation details between pages of our website.
• Tableless design is more beneficial for SEO because it is tree type layout.

NOTE: This front end developer interview questions is the most commonly asked. Make sure to study in detail this.

• Video and Audio: Video and Audio are the new tags that allow these features to embed into the website.
• Nav: This element is used for that part of the internet site that links to different pages at the websites.
• Canvas: Canvas is a new feature of HTML5 which is used to draw images.
• Footer: It is used to define the footer of a document or any section.
• Placeholders: It gives hints to the user as to what is to be inserted in a particular field.

It is a CSS property which is used to clear of an floating elements are not allowed to float. Its default value is "none". We can also use "clear:left" or "clear:right"