Top 30 Frontend Web Development Interview Questions and answers with Programing Code


1.What is HTML and what are its basic components?

HTML stands for Hyper Text Markup Language. It is the standard markup language used to create web pages. The basic components of HTML are tags, attributes, and values. Tags are used to define different parts of a web page, such as headings, paragraphs, and links. Attributes provide additional information about a tag, such as the color of text or the URL of a link. Values are used to specify the content of a tag, such as the text of a heading or the destination of a link.

2.What is CSS and how does it work?

CSS stands for Cascading Style Sheets. It is a style sheet language used to describe the presentation of a document written in HTML. CSS works by separating the content of a web page from its presentation. This allows developers to define styles once and apply them to multiple elements throughout the page. CSS can be used to define styles for text, colors, layout, and many other aspects of a web page.

3.What is JavaScript and what are its basic features?

JavaScript is a programming language used to create interactive web pages. Its basic features include variables, operators, functions, and conditional statements. Variables are used to store data, such as numbers or strings of text. Operators are used to perform operations on data, such as addition or comparison. Functions are used to perform a specific task, such as updating the content of a web page. Conditional statements are used to make decisions based on the value of data, such as displaying a message if a user enters an incorrect password.

4.What is a doctype and why is it important?

A doctype is a declaration that specifies the version of HTML being used in a web page. It is important because different versions of HTML have different rules and syntax. By including a doctype, web browsers know how to interpret the content of the page and ensure that it is displayed correctly.

5.What is the difference between HTML and XHTML?

HTML and XHTML are both markup languages used to create web pages. The main difference between the two is that XHTML is stricter and more structured than HTML. XHTML requires that all tags be properly nested and closed, and that all attributes have values. HTML is more forgiving and allows for looser syntax.

6.What is the difference between an inline element and a block element?

An inline element is an HTML element that does not start on a new line and only takes up as much space as necessary. Examples of inline elements include the span and anchor tags. A block element is an HTML element that starts on a new line and takes up the full width of its parent element. Examples of block elements include the div and p tags.

7.What is the difference between the visibility property and the display property in CSS?

The visibility property in CSS controls whether an element is visible or hidden. When an element is hidden, it still takes up space on the page. The display property in CSS controls how an element is displayed on the page. When an element is set to display: none, it is completely removed from the page and does not take up any space.

8.What is the box model in CSS?

The box model in CSS is a way of representing the layout of an HTML element. It consists of four parts: content, padding, border, and margin. The content area is where the actual content of the element is displayed. The padding area is the space between the content and the border. The border is the line that surrounds the content and padding. The margin is the space between the border and the next element on the page.

9.What is responsive design and why is it important?

Responsive design is a design approach that allows a website to adjust its layout and content based on the size of the screen it is being viewed on. This ensures that the website is optimized for all devices, including desktops, laptops, tablets, and smartphones. Responsive design is important because more and more people are accessing the internet on mobile devices, and a website that is not optimized for mobile can lead to a poor user experience.

10.What is a media query in CSS and how does it work?

A media query in CSS is a technique used to apply different styles to a web page based on the size of the screen or device it is being viewed on. It works by checking the width of the screen and applying styles accordingly. For example, a media query may apply a different font size or layout to a page when it is viewed on a mobile device compared to a desktop computer.

11.What is a CSS framework and give examples of some popular CSS frameworks?

A CSS framework is a pre-built set of CSS files and code that can be used to speed up the development of a website. Examples of popular CSS frameworks include Bootstrap, Foundation, and Materialize.

12.What is a responsive grid system in CSS and how does it work?

A responsive grid system in CSS is a technique used to create a flexible layout for a web page that adjusts to different screen sizes. It works by dividing the page into a grid of columns and rows, and allowing elements to be placed within those columns and rows. The number of columns and their widths can be adjusted based on the size of the screen, ensuring that the layout remains consistent and easy to read.

13.What is a CSS preprocessor and give examples of some popular CSS preprocessors?

A CSS preprocessor is a tool that allows developers to write CSS code in a more efficient and organized way. Examples of popular CSS preprocessors include Sass, Less, and Stylus.

14.What is a polyfill in JavaScript and why is it important?

A polyfill in JavaScript is a piece of code that adds support for a feature or functionality that is not supported in all web browsers. It is important because not all web browsers support the same features and functionalities, and a website that relies on a feature that is not supported in all browsers may not function properly for some users.

15.What is an event in JavaScript and give examples of some common events?

An event in JavaScript is an action that occurs on a web page, such as a click, hover, or keypress. Examples of some common events include click, hover, keypress, and scroll.

16.What is the difference between null and undefined in JavaScript?

Null and undefined are both values in JavaScript that represent the absence of a value. Null is a deliberate value that is assigned to a variable or property to indicate that it has no value. Undefined is a value that is automatically assigned to a variable or property when it has not been initialized or does not exist.

17.What is a callback function in JavaScript and how does it work?

A callback function in JavaScript is a function that is passed as an argument to another function and is called when that function is executed. It works by allowing developers to write code that is executed asynchronously, meaning that it is executed at a later time after other code has finished executing.

18.What is the difference between == and === in JavaScript?

The == operator in JavaScript is used to compare two values for equality, and will perform type coercion if necessary. The === operator, on the other hand, is used to compare two values for equality, but will not perform type coercion. This means that the === operator will only return true if both values have the same data type and value.

19.What is the difference between let and var in JavaScript?

Let and var are both keywords used to declare variables in JavaScript. The main difference between the two is that var has function scope, meaning that it can be accessed from anywhere within the function it was declared in, while let has block scope, meaning that it can only be accessed within the block it was declared in.

20.What is the difference between synchronous and asynchronous programming in JavaScript?

Synchronous programming in JavaScript refers to code that is executed sequentially, meaning that each line of code is executed in order and the program waits for each line to complete before moving on to the next. Asynchronous programming, on the other hand, refers to code that is executed non-sequentially, meaning that multiple lines of code can be executed at the same time, and the program does not wait for each line to complete before moving on to the next.

21.What is a Promise in JavaScript and how does it work?

A Promise in JavaScript is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It works by allowing developers to write code that is executed asynchronously, and then to handle the eventual outcome of that code (either success or failure) using a Promise object.

22.What is a closure in JavaScript and give an example?

A closure in JavaScript is a function that has access to variables in its outer (enclosing) function's scope, even after the outer function has returned. An example of a closure in JavaScript is as follows:

function outerFunction() {

var outerVariable = "Hello, ";


function innerFunction(name) {

console.log(outerVariable + name + "!");

}

return innerFunction;

}

var sayHello = outerFunction();

sayHello("Alice"); // Output: "Hello, Alice!"

In this example, the innerFunction has access to the outerVariable even after the outerFunction has returned, because the sayHello variable is still referencing the innerFunction.

23.What is the Document Object Model (DOM) and how does it work?

The Document Object Model (DOM) is a programming interface for HTML and XML documents. It represents the web page as a tree-like structure of nodes and allows developers to manipulate the content and structure of the web page using JavaScript. For example, developers can use the DOM to add or remove elements from the page, change the text of an element, or respond to user interactions like clicks and hovers.

24.What is an API and how does it work?

An API, or Application Programming Interface, is a set of protocols, routines, and tools for building software applications. It provides a way for different applications to communicate with each other and share data or functionality. For example, a web application may use an API to access data from a remote server or to perform a specific task, like sending an email.

25.What is AJAX and how does it work?

AJAX, or Asynchronous JavaScript and XML, is a technique used to create fast and dynamic web pages without requiring a full page reload. It works by using JavaScript to send requests to a server in the background and then updating the page with the response without requiring a full page reload. This allows web pages to update content quickly and without interruption, providing a smoother user experience.

26.What is the difference between a GET request and a POST request in AJAX?

A GET request is used to retrieve data from a server, while a POST request is used to send data to a server. In a GET request, the data is appended to the URL as query parameters, while in a POST request, the data is sent in the request body.

27.What is a callback function in JavaScript and give an example?

A callback function in JavaScript is a function that is passed as an argument to another function and is executed after some operation is completed. An example of a callback function in JavaScript.

28.What is a higher-order function in JavaScript and give an example?

A higher-order function in JavaScript is a function that takes one or more functions as arguments, or returns a function as its result. An example of a higher-order function in JavaScript is as follows:

function multiplyBy(factor) {

return function(number) {

return number * factor;

};

}

var double = multiplyBy(2);

var triple = multiplyBy(3);

console.log(double(5)); // Output: 10

console.log(triple(5)); // Output: 15

In this example, the multiplyBy function takes a factor as an argument and returns a new function that takes a number as an argument and multiplies it by the factor. The returned function can be used to create new functions that multiply by different factors, like double and triple in this example.

29.What is hoisting in JavaScript and how does it work?

Hoisting in JavaScript is a behavior where variable and function declarations are moved to the top of their respective scopes, regardless of where they are actually defined in the code. This means that a variable or function can be used before it is declared, as long as it is declared in the same scope. For example:

console.log(x); // Output: undefined

var x = 10;

In this example, the variable x is used before it is declared, but because of hoisting, it is still defined and has the value undefined at the time it is used.

30.What is a template literal in JavaScript and how does it work?

A template literal in JavaScript is a string literal that allows for embedded expressions and multiline strings. It is delimited by backticks (`) instead of quotes, and expressions are enclosed in ${...}. For example:

var name = "Alice";

var age = 30;

console.log(My name is ${name} and I am ${age} years old.);

In this example, the template literal allows for the embedded expressions ${name} and ${age} to be evaluated and included in the string that is logged to the console.