Web Developer Interview Questions and Answers

Ques 1. Explain the box model in CSS.

The box model consists of content, padding, border, and margin. It defines the spacing and dimensions of an element.

Example:

div {
  width: 200px;
  padding: 20px;
  border: 2px solid black;
  margin: 10px;
}

Ques 2. What is the difference between 'GET' and 'POST' HTTP methods?

'GET' is used to request data from a specified resource, while 'POST' is used to submit data to be processed to a specified resource.

Ques 3. Explain the purpose of the 'box-sizing' property in CSS.

The 'box-sizing' property defines how the width and height of an element are calculated, including the padding and border, or excluding them.

Example:

div {
  box-sizing: border-box;
}

Ques 4. What is the purpose of the 'cookie' in web development?

Cookies are small pieces of data stored on the client's machine, used to store user information and maintain state between HTTP requests.

Example:

document.cookie = 'username=John; expires=Thu, 18 Dec 2024 12:00:00 UTC; path=/';

Ques 5. What is the difference between 'localStorage' and 'sessionStorage'?

'localStorage' stores data with no expiration time, while 'sessionStorage' stores data for the duration of the page session.

Ques 6. What is the role of the 'DOCTYPE' declaration in HTML?

The 'DOCTYPE' declaration defines the document type and version of HTML or XHTML, ensuring proper rendering in web browsers.

Example:

Ques 7. What is the 'CSS Box Model'?

The CSS Box Model is a design and layout concept that consists of content, padding, border, and margin, defining the space around and within an HTML element.

Ques 8. Explain the difference between 'localStorage' and 'sessionStorage'.

'localStorage' persists even when the browser is closed and reopened, while 'sessionStorage' data is only available for the duration of the page session.

Ques 9. What is the 'DRY' principle in software development?

DRY (Don't Repeat Yourself) is a software development principle advocating for reducing redundancy by reusing code and avoiding duplication.

Ques 10. What is the role of the 'meta' tag with the 'charset' attribute in HTML?

The 'meta' tag with the 'charset' attribute specifies the character encoding for the HTML document, ensuring proper text rendering.

Example:

Ques 11. What is the 'event.preventDefault()' method in JavaScript used for?

'event.preventDefault()' is used to prevent the default behavior associated with an event, such as preventing a form submission or a link from navigating.

Example:

document.getElementById('myForm').addEventListener('submit', function(event) {
  event.preventDefault();
  // additional handling code
});

Ques 12. What is the difference between HTML and XHTML?

HTML is more forgiving and allows for more flexibility, while XHTML is stricter and follows XML syntax.

Example:

HTML: 
Hello World

XHTML: 
Hello World

Ques 13. What is the purpose of the 'defer' attribute in a script tag?

The 'defer' attribute delays the execution of a script until the HTML parsing is complete.

Example:

Ques 14. Differentiate between sessionStorage and localStorage in HTML5.

sessionStorage stores data for the duration of a page session, while localStorage stores data with no expiration time.

Example:

sessionStorage.setItem('key', 'value');
localStorage.setItem('key', 'value');

Ques 15. How does CSS specificity work?

Specificity determines which CSS rule takes precedence when multiple conflicting rules target the same element.

Example:

div#myId {
  color: blue;
}
#myId {
  color: red;
}

Ques 16. What is responsive web design?

Responsive web design ensures that web applications render well on various devices and window or screen sizes.

Example:

@media screen and (max-width: 600px) {
  body {
    background-color: lightblue;
  }
}

Ques 17. What is the purpose of the 'this' keyword in JavaScript?

The 'this' keyword refers to the current execution context and allows access to properties and methods of the current object.

Example:

const person = {
  name: 'John',
  greet: function() {
    console.log('Hello, ' + this.name + '!');
  }
};
person.greet();

Ques 18. Explain the concept of CORS (Cross-Origin Resource Sharing).

CORS is a security feature implemented by web browsers to restrict web pages from making requests to a different domain than the one that served the web page.

Ques 19. What is the purpose of the 'async' and 'await' keywords in JavaScript?

The 'async' keyword is used to declare an asynchronous function, and 'await' is used to pause the execution of the function until the Promise is settled.

Example:

async function fetchData() {
  let response = await fetch('https://api.example.com/data');
  let data = await response.json();
  console.log(data);
}

Ques 20. How does the 'localStorage' differ from 'sessionStorage' in HTML5?

'localStorage' persists even when the browser is closed and reopened, while 'sessionStorage' data is only available for the duration of the page session.

Ques 21. What is the significance of the 'viewport' meta tag in HTML?

The 'viewport' meta tag controls the layout and scaling of the webpage on mobile devices, ensuring proper rendering on various screen sizes.

Example:

Ques 22. What are RESTful APIs, and how do they work?

RESTful APIs (Representational State Transfer) are web APIs that adhere to the principles of REST, utilizing standard HTTP methods for communication.

Ques 23. What is the purpose of the 'defer' attribute in a script tag?

The 'defer' attribute delays the execution of a script until the HTML parsing is complete.

Example:

Ques 24. Explain the concept of 'hoisting' in JavaScript.

Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase.

Example:

console.log(x); // undefined
var x = 5;

Ques 25. Explain the 'same-origin policy' in the context of web security.

The 'same-origin policy' is a security measure that restricts web pages from making requests to a different domain than the one that served the web page.

Ques 26. How does the 'target' attribute work in HTML forms?

The 'target' attribute specifies where to open the linked document when submitting a form, such as '_blank' to open in a new tab.

Example:

Ques 27. Explain the concept of 'Promises' in JavaScript.

Promises are objects representing the eventual completion or failure of an asynchronous operation, allowing better handling of asynchronous code.

Example:

const fetchData = new Promise((resolve, reject) => {
  // asynchronous code
});

Ques 28. Explain the purpose of the 'data-*' attribute in HTML.

The 'data-*' attribute is used to store custom data private to the page or application, accessible by JavaScript and CSS.

Example:

User Profile