Java Script Concepts

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

• var is block-scoped, let is block-scoped, and const is function-scoped but can be reassigned.

• var is block-scoped, let is function-scoped, and const is block-scoped but cannot be reassigned.

• var is function-scoped, let is block-scoped, and const is block-scoped but cannot be reassigned.

• var is block-scoped, let is block-scoped, and const is block-scoped but can be reassigned.

Explain the difference between == and === in JavaScript.

• == checks for equality after type coercion, while === checks for strict equality without type coercion.

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

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

• == checks for strict equality without type coercion, while === checks for equality after type coercion.

How do you loop through an array in JavaScript?

• map method: array.map(item => { // access item })

• while loop: let i = 0; while(i < array.length) { // access array[i]; i++; }

• do...while loop: let i = 0; do { // access array[i]; i++; } while(i < array.length)

• for loop: for(let i = 0; i < array.length; i++) { // access array[i] } forEach method: array.forEach(item => { // access item }) for...of loop: for(const item of array) { // access item }

What is the purpose of a function in JavaScript?

• The purpose of a function in JavaScript is to encapsulate a block of code that can be executed whenever needed.

• The purpose of a function in JavaScript is to slow down code execution

• The purpose of a function in JavaScript is to increase file size unnecessarily

• The purpose of a function in JavaScript is to confuse developers

How do you define an object in JavaScript?

• const obj = { key1: value1, key2: value2 };

• const obj = { key1 = value1, key2 = value2 };

• const obj = (key1: value1, key2: value2);

• const obj = [key1: value1, key2: value2];

Explain the concept of DOM Manipulation in JavaScript.

• DOM Manipulation is only possible by reloading the entire webpage.

• DOM Manipulation is used to create static web pages that do not change based on user interactions.

• DOM Manipulation allows developers to dynamically update the webpage based on user interactions, data changes, or other events without needing to reload the entire page.

• DOM Manipulation is a feature exclusive to CSS and cannot be achieved with JavaScript.

What is event handling in JavaScript?

• Event handling in JavaScript is the process of generating random numbers.

• Event handling in JavaScript is the process of styling HTML elements.

• Event handling in JavaScript is the process of capturing and responding to user interactions or system events.

• Event handling in JavaScript is the process of creating animations on a webpage.

What is a callback function in JavaScript?

• A callback function in JavaScript is a function that is passed as an argument to another function and is executed after some operation has been completed.

• A callback function in JavaScript is a function that is not passed as an argument to another function.

• A callback function in JavaScript is a function that is executed before some operation has been completed.

• A callback function in JavaScript is a function that is only used for error handling.

How does the 'await' keyword work in JavaScript?

• The 'await' keyword skips the async function execution and moves to the next line of code

• The 'await' keyword pauses the async function execution and waits for the Promise to be settled.

• The 'await' keyword throws an error if the Promise is not resolved within a specific time frame

• The 'await' keyword can only be used with synchronous functions

Explain the concept of asynchronous programming in JavaScript.

• Asynchronous programming in JavaScript only allows tasks to run sequentially within the main program flow.

• Asynchronous programming in JavaScript enables tasks to run separately from the main program flow, preventing blocking behavior.

• Asynchronous programming in JavaScript causes the program to freeze until all tasks are completed.

• Asynchronous programming in JavaScript is not supported by modern browsers.