JavaScript Interview Questions Answers

In this blog post, we will discuss JavaScript Interview questions answers (2023), (Java Interview Questions Answers), here we have provided you top 30 questions and answers related to JavaScript programming language, which are asked in interview, that is important for freshers. If you go for an interview in any IT sector company, then all these questions are definitely asked. That’s why we have prepared top 30 questions and answers for you on this blog related Java Programming Language.

JavaScript Interview Questions and Answers (2023)

Question 1. What is JavaScript?

Answer: JavaScript is a widely-used programming language that allows developers to add dynamic content and interactivity to web pages.

 

Question 2. What are the different data types in JavaScript?

Answer: JavaScript has six primitive data types: string, number, boolean, null, undefined, and symbol. It also has an object data type.

 

Question 3. How do you declare variables in JavaScript?

Answer: You can declare variables in JavaScript using the keywords var, let, or const.

 

Question 4. What is the difference between let, const, and var in JavaScript?

Answer: “let and const” are block-scoped and can be reassigned and redeclared within their scope, while const is a constant variable that cannot be reassigned. var is function-scoped and can be hoisted, and it can also be reassigned and redeclared within its scope.

Question 5. How do you create an object in JavaScript?

Answer: You can create an object in JavaScript using object literal syntax, constructor functions, or ES6 classes.

 

Question 6. What are closures in JavaScript?

Answer: Closures are functions that have access to variables from their surrounding lexical environment even after the outer function has executed.

 

Question 7. Explain callback functions in JavaScript.

Answer: Callback functions are functions that are passed as arguments to other functions and are executed after the completion of a particular task.

 

Question 8. What is event delegation in JavaScript?

Answer: Event delegation is a technique where you attach an event handler to a parent element instead of individual child elements, which allows you to handle events for dynamically added elements.

 

Question 9. What are arrow functions in JavaScript and how do they differ from regular functions?

Answer: Arrow functions are a concise syntax for writing functions in JavaScript that have lexical scoping of this and do not bind their own this, arguments, or super values. They are more concise and have some differences in behavior compared to regular functions, such as not having their own this and not being able to be used as constructors.

 

Question 10. What is “this” keyword in JavaScript?

Answer: “this” refers to the current object that the function is a part of, and its value is determined at runtime depending on how the function is invoked.




Question 11. Explain the concept of prototypal inheritance in JavaScript.

Answer: In JavaScript, objects inherit properties and methods from their prototypes, which allows for object-based inheritance.

 

Question 12. What are arrow functions in JavaScript?

Answer: Arrow functions are a concise syntax for writing functions in JavaScript that have lexical scoping of this and do not bind their own this, arguments, or super values.

 

Question 13. What is event bubbling and event capturing in JavaScript?

Answer: Event bubbling is the process where an event that is triggered on a nested element propagates up to its parent elements, while event capturing is the process where an event is captured by the parent elements before reaching the target element.

 

Question 14. What is the difference between null and undefined in JavaScript?

Answer: “null” represents the absence of a value, while undefined represents the absence of a value being assigned to a variable or the absence of a return value from a function.

 

Question 15. What is a promise in JavaScript?

Answer: A promise is a JavaScript object that represents the eventual completion or failure of an asynchronous operation and allows for handling asynchronous operations in a more readable and manageable way.

JavaScript Interview Questions and Answers (2023)

Question 16. What is event handling in JavaScript?

Answer: Event handling is the process of writing code to respond to events triggered by user interactions or other actions in a web page, such as clicking a button or submitting a form.

 

Question 17. What is the use of the bind() method in JavaScript?

Answer: The bind() method in JavaScript is used to create a new function that has a specified this value and, optionally, a fixed set of arguments, which is useful for setting the context of a function.

 

Question 18. What are the different ways to loop through an array in JavaScript?

Answer: You can loop through an array in JavaScript using for loops, forEach() method, for…of loop, and for…in loop.




Question 19. What is the purpose of the localStorage and sessionStorage objects in JavaScript?

Answer: localStorage and sessionStorage are web storage objects in JavaScript that allow you to store key-value pairs in a web browser. localStorage stores data with no expiration time, while sessionStorage stores data that is accessible only for the duration of the current session.

 

Question 20. Explain the concept of “hoisting” in JavaScript.

Answer: Hoisting is a mechanism in JavaScript where variable declarations and function declarations are moved to the top of their respective scopes during the compilation phase, allowing them to be accessed before their actual declaration.

 

Question 21. How do you handle errors in JavaScript?

Answer: Errors in JavaScript can be handled using try, catch, and finally blocks. You can also throw custom errors using the throw statement.

 

Question 22. What are the different ways to create objects in JavaScript?

Answer: You can create objects in JavaScript using object literals, constructor functions, Object.create(), and ES6 classes.

 

Question 23. How do you handle asynchronous programming in JavaScript?

Answer: Asynchronous programming in JavaScript can be handled using callbacks, promises, and async/await syntax. Callbacks are the traditional way of handling asynchronous operations, promises provide a more organized and manageable way of handling async code, and async/await syntax provides a more synchronous-looking way of handling asynchronous operations using promises.

 

Question 24. What is event propagation in JavaScript and how does it work?

Answer: Event propagation refers to the process by which an event is passed from the target element to its parent elements in the DOM tree. It can occur in two directions: capturing phase (from the top of the tree to the target element) and bubbling phase (from the target element to the top of the tree).

 

Question 25. What is event delegation in JavaScript?

Answer: Event delegation is a technique where you attach an event handler to a parent element instead of individual child elements, which allows you to handle events for dynamically added elements.

 

Question 26. How do you clone an object in JavaScript?

Answer: You can clone an object in JavaScript using various methods such as Object.assign(), spread syntax (…), and JSON.parse(JSON.stringify()).

 

Question 27. What are the different types of error handling in JavaScript?

Answer: There are two types of error handling in JavaScript: synchronous error handling using try, catch, and finally blocks, and asynchronous error handling using promises and catch() method.




Question 28. What is a closure in JavaScript and how does it work?

Answer: A closure is a function that has access to variables from its outer (enclosing) lexical scope, even after the outer function has completed execution. It allows for maintaining private data and creating higher-order functions in JavaScript.

Question 29. What are arrow functions in JavaScript and how do they differ from regular functions?

Answer: Arrow functions are a concise syntax for writing functions in JavaScript that have lexical scoping of this and do not bind their own this, arguments, or super values. They are more concise and have some differences in behavior compared to regular functions, such as not having their own this and not being able to be used as constructors.

 

Question 30. How do you handle asynchronous programming in JavaScript?

Answer: Asynchronous programming in JavaScript can be handled using callbacks, promises, and async/await syntax. Callbacks are the traditional way of handling asynchronous operations, promises provide a more organized and manageable way of handling async code, and async/await syntax provides a more synchronous-looking way of handling asynchronous operations using promises.

 

So, you learned here Top 30 JavaScript Interview Questions Answers (2023), all these questions are very important, if you are from IT sector. I hope you have understood all questions and answers very well and if you have any doubt, regarding it then you can ask in the comment section.

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