Javascript

Question 1

Is JavaScript a multithreaded language?

Answer 1

No, JavaScript is single-threaded.

Question 2

What is a web worker?

Answer 2

A Web Worker in JavaScript is used to run scripts in the background, separate from the main execution thread of a web page. This allows the main thread (UI thread) to remain responsive while executing potentially time-consuming tasks such as data processing, computations, or API requests.

• Improves performance: Offloads CPU-intensive tasks from the main thread.
• Prevents UI freezing: Keeps the UI responsive while running heavy operations.
• Parallel execution: Enables multi-threading-like behavior in JavaScript.

Question 3

True or False: Web workers can directly manipulate the DOM.

Answer 3

False

Question 4

Fill in the blank: TypeScript is a superset of __________.

Answer 4

JavaScript

Question 5

What is one major difference between JavaScript and TypeScript?

Answer 5

TypeScript includes static typing, while JavaScript is dynamically typed.

Question 6

What is JavaScript primarily used for?

Answer 6

JavaScript is primarily used for creating interactive and dynamic content on websites.

Question 7

True or False: JavaScript is a server-side programming language.

Answer 7

False: JavaScript is primarily a client-side programming language, although it can also be used on the server-side with environments like Node.js.

Question 8

Fill in the blank: JavaScript is a _____-typed language.

Answer 8

dynamically

Question 9

What does the ‘var’ keyword do in JavaScript?

Answer 9

The ‘var’ keyword declares a variable that can be re-assigned and has function scope.

Question 10

What is the purpose of the ‘let’ keyword in JavaScript?

Answer 10

The ‘let’ keyword declares a block-scoped variable that can be re-assigned.

Question 11

What is a JavaScript function?

Answer 11

A JavaScript function is a block of code designed to perform a particular task and can be executed when called.

Question 12

Multiple Choice: Which of the following is NOT a JavaScript data type? A) String B) Object C) Number D) Class

Answer 12

D) Class

Question 13

What is the use of ‘const’ in JavaScript?

Answer 13

‘const’ declares a block-scoped variable that cannot be re-assigned.

Question 14

True or False: JavaScript supports object-oriented programming.

Answer 14

True: JavaScript supports object-oriented programming through prototypes and classes.

Question 15

What is the purpose of the ‘this’ keyword in JavaScript?

Answer 15

‘this’ refers to the context in which a function is executed, typically the object that is calling the function.

Question 16

What is an array in JavaScript?

Answer 16

An array is a data structure that can hold multiple values in a single variable, indexed by numbers.

Question 17

What are JavaScript objects?

Answer 17

JavaScript objects are collections of key-value pairs that can store data and functions.

Question 18

Fill in the blank: JavaScript uses _____ to handle asynchronous operations.

Answer 18

promises

Question 19

What is the purpose of the ‘map’ method in JavaScript?

Answer 19

The ‘map’ method creates a new array populated with the results of calling a provided function on every element in the calling array.

Question 20

Multiple Choice: Which of the following is a JavaScript framework? A) Angular B) HTML C) CSS D) SQL

Answer 20

A) Angular

Question 21

What is event bubbling in JavaScript?

Answer 21

Event bubbling is a type of event propagation where an event starts from the target element and bubbles up to the root.

Question 22

What does ‘JSON’ stand for?

Answer 22

JSON stands for JavaScript Object Notation, a lightweight data interchange format.

Question 23

True or False: JavaScript can manipulate HTML and CSS.

Answer 23

True: JavaScript can be used to manipulate HTML elements and apply CSS styles dynamically.

Question 24

What is the ‘DOMContentLoaded’ event in JavaScript?

Answer 24

The ‘DOMContentLoaded’ event is fired when the initial HTML document has been completely loaded and parsed.

Question 25

Fill in the blank: In JavaScript, _____ functions are functions defined within another function.

Answer 25

nested

Question 26

What is a closure in JavaScript?

Answer 26

A closure is a function that retains access to its lexical scope, even when the function is executed outside that scope. Closures occur when a function is **defined inside another function** and retains access to the **outer function's variables** even after the outer function has finished executing.

Question 27

What is the difference between '==' and '===' in JavaScript?

Answer 27

'==' checks for equality with type coercion, while '===' checks for strict equality without type coercion.

Question 28

What is the purpose of the 'async' keyword in JavaScript?

Answer 28

'async' is used to declare an asynchronous function that returns a promise.

Question 29

What is the 'fetch' API used for in JavaScript?

Answer 29

The 'fetch' API is used to make network requests to servers and handle responses.

Question 30

Multiple Choice: Which of the following is a method to loop through an array in JavaScript? A) forEach B) loop C) iterate D) traverse

Answer 30

A) forEach

Question 31

What is type coercion in JavaScript?

Answer 31

Type coercion in JavaScript is the automatic conversion of values from one data type to another when an operation involves different types. JavaScript is a loosely typed language, meaning it can implicitly convert data types to make expressions work.

Question 32

What is useReducer in React?

Answer 32

In JavaScript, particularly in React, useReducer is a React Hook used for managing complex state logic in a component. It is an alternative to useState, especially when the state transitions involve multiple sub-values or when the next state depends on the previous state.

Question 33

How does the event loop work in JavaScript?

Answer 33

The JavaScript event loop manages asynchronous tasks by coordinating the call stack, task queue, and microtask queue. Synchronous code runs first, while asynchronous tasks (like setTimeout, fetch, and event listeners) are handled by the browser and queued. Microtasks (Promises, MutationObserver) have higher priority and execute before regular tasks from the callback queue. The event loop continuously checks if the call stack is empty before processing queued tasks. This ensures non-blocking execution and smooth performance in JavaScript.

Question 34

What are the 3 types of scope in JavaScript? Explain each

Answer 34

JS follows a hierarchical scope chain Local Enclosing Global Local scope: inside the function itself Enclosing: inside the outer function Global: in the top-level script JS uses lexical scope - the scope in which variables and functions are defined, where they appear in the code at the time of writing (not running)

Question 35

Explain lexical scoping

Answer 35

JS follows lexical scoping - variable resolution is based on where the function is defined, not where it is called