Asynchronous JavaScript Programming: Enhance Web Responsiveness

Question 1

What is the primary purpose and functionality of the async/await keywords in JavaScript?

Accepted Answer

To simplify asynchronous code by providing a synchronous-like syntax

Answer

To create new threads for faster execution

Answer

To automatically handle errors in asynchronous operations

Answer

To make asynchronous code more efficient

Question 2

Which of the following is NOT a benefit of using async/await?

Accepted Answer

Increased code complexity

Answer

Improved code readability and error handling

Answer

Reduced need for callback functions

Answer

Better performance

Question 3

What is the primary purpose of using a Promise.all() method in JavaScript?

Accepted Answer

To execute multiple Promises concurrently and return a single Promise that resolves or rejects when all the input Promises have settled.

Answer

To handle errors that occur in any of the input Promises.

Answer

To cancel all the input Promises if one of them rejects.

Answer

To create a new Promise that resolves after a specified amount of time.

Question 4

When would asynchronous programming in JavaScript be most advantageous?

Accepted Answer

Enabling a user to scroll through a webpage while a large image loads

Accepted Answer

Awaiting a server response after sending a request

Answer

Performing a lengthy computation that takes several seconds

Question 5

Which of the following is NOT a type of asynchronous operation commonly used in JavaScript?

Accepted Answer

Synchronous functions

Answer

Callbacks

Answer

Promises

Answer

Async/await

Question 6

What is the main purpose of a callback function in asynchronous programming?

Accepted Answer

To handle the result (success or failure) of an asynchronous operation when it completes.

Answer

To create a new asynchronous operation.

Answer

To stop the execution of the program until the asynchronous operation completes.

Answer

To define the type of data returned by an asynchronous operation.

Question 7

What is the key difference between a resolved and a rejected Promise?

Accepted Answer

A resolved Promise represents a successful operation, while a rejected Promise represents an unsuccessful operation or error.

Answer

A rejected Promise represents a successful operation, while a resolved Promise represents an unsuccessful operation or error.

Answer

A resolved Promise can handle both successful and failed operations.

Answer

A rejected Promise can handle both successful and failed operations.

Question 8

What is the primary function of the event loop in asynchronous programming?

Accepted Answer

To monitor for and handle asynchronous events (e.g., callbacks) and execute them when appropriate.

Answer

To create separate threads for each asynchronous operation to prevent blocking the main thread.

Answer

To prevent the browser from freezing while waiting for asynchronous operations to complete.

Answer

To store data related to asynchronous operations.

Question 9

The fetch() method in JavaScript is primarily used to:

Accepted Answer

Perform network requests and retrieve data.

Answer

Create new Promises.

Answer

Handle asynchronous events.

Answer

Update the user interface.

Question 10

Which of the following is NOT a type of asynchronous operation in JavaScript?

Accepted Answer

Synchronous functions

Answer

Callbacks

Answer

Promises

Answer

Events

Question 11

Callbacks in asynchronous programming serve the purpose of:

Accepted Answer

Executing code after an asynchronous operation completes.

Answer

Executing code before an asynchronous operation completes.

Answer

Preventing an asynchronous operation from executing.

Answer

Creating a new thread of execution.

Question 12

Promises in asynchronous programming provide which key benefit?

Accepted Answer

Improved code readability and error handling.

Answer

Faster execution of asynchronous operations.

Answer

Simplified integration with synchronous code.

Answer

Reduced memory usage.

Question 13

In Promises, the 'then' and 'catch' methods have distinct roles. How would you describe their difference?

Accepted Answer

'then' handles successful outcomes, while 'catch' handles errors.

Answer

'catch' handles successful outcomes, while 'then' handles errors.

Answer

Both 'then' and 'catch' handle successful outcomes.

Answer

Both 'then' and 'catch' handle errors.

Question 14

What is the primary purpose of the 'await' keyword in asynchronous programming?

Accepted Answer

To pause execution of a function until an asynchronous operation completes.

Answer

To create a new asynchronous operation.

Answer

To execute a synchronous function.

Answer

To handle errors in asynchronous operations.

Question 15

In which scenarios is it appropriate to consider using asynchronous programming in JavaScript?

Accepted Answer

In all of the mentioned scenarios.

Answer

When performing long-running operations without hindering the main thread.

Answer

When making multiple HTTP requests concurrently.

Answer

When improving the responsiveness of a web application.

Question 16

The fundamental distinction between synchronous and asynchronous code in JavaScript is:

Accepted Answer

Synchronous code blocks the main thread, while asynchronous code does not.

Answer

Synchronous code executes immediately, while asynchronous code executes later.

Answer

Asynchronous code executes immediately, while synchronous code executes later.

Answer

Asynchronous code blocks the main thread, while synchronous code does not.

Question 17

What is the primary purpose of using callback functions in asynchronous programming?

Accepted Answer

To execute code when an asynchronous operation completes

Answer

To define the asynchronous operation to be performed

Answer

To store the result of an asynchronous operation

Answer

To interrupt the execution of the main program

Question 18

What is the correct syntax for defining an asynchronous function using async/await?

Accepted Answer

async function myAsyncFunction() { ... }

Answer

function async myAsyncFunction() { ... }

Answer

myAsyncFunction async function() { ... }

Answer

myAsyncFunction() async function { ... }

Question 19

What is the primary function of the 'then()' method in JavaScript promises?

Accepted Answer

Executing a callback function when the promise is resolved

Answer

Handling errors that occur during promise execution

Answer

Chaining multiple promises together

Answer

Canceling the execution of a promise

Question 20

Which of these is NOT a valid state for a JavaScript promise?

Accepted Answer

Fulfilled

Answer

Pending

Answer

Resolved

Answer

Rejected

Question 21

In JavaScript, the event loop is responsible for:

Accepted Answer

Executing pending tasks continuously.

Answer

Storing asynchronous operations.

Answer

Running as a separate thread alongside the main program.

Answer

Creating custom events.

Question 22

Which approach is commonly used to manage asynchronous operations in JavaScript?

Accepted Answer

Employing callbacks

Answer

Using the wait() function

Answer

Implementing try-catch blocks

Answer

Pausing code execution using sleep()

Question 23

What is the primary purpose of promises in JavaScript?

Accepted Answer

Handling asynchronous operations and representing their eventual outcome.

Answer

Pausing code execution until an operation is complete.

Answer

Creating chains of asynchronous operations.

Answer

Managing errors in asynchronous operations.

Question 24

Which method is NOT available for a promise object?

Accepted Answer

resolve()

Answer

then()

Answer

catch()

Answer

finally()

Question 25

Which syntax is correct for defining an asynchronous function using the async keyword?

Accepted Answer

async function myFunction() {}

Answer

function async myFunction() {}

Answer

myFunction async function() {}

Answer

async myFunction function() {}

Question 26

What is the main advantage of using the await keyword in asynchronous functions?

Accepted Answer

It allows code to pause and wait for an asynchronous operation to complete before continuing.

Answer

It transforms an asynchronous function into a synchronous one.

Answer

It ensures that asynchronous operations are executed in a specific order.

Answer

It enhances code readability and simplifies debugging.

Question 27

How can you differentiate between a fulfilled and a rejected promise?

Accepted Answer

A fulfilled promise represents a successful asynchronous operation, while a rejected promise represents an error.

Answer

A fulfilled promise is always returned before a rejected promise.

Answer

A rejected promise cannot be handled.

Answer

Promises cannot exist in both fulfilled and rejected states.

Question 28

What is the key performance drawback of blocking asynchronous operations in JavaScript?

Accepted Answer

Degraded user interface responsiveness and performance issues

Answer

Improved code readability and maintainability

Answer

Negligible impact on performance

Answer

Enhanced code robustness and error handling

Question 29

In asynchronous programming, which of the following is a crucial concept?

Accepted Answer

Callbacks

Answer

Loops

Answer

Variables

Answer

Arrays

Question 30

What is the primary purpose of a Promise object in asynchronous programming?

Accepted Answer

To manage asynchronous operations and their outcomes

Answer

To store data in memory

Answer

To create event listeners

Answer

To perform mathematical calculations

Question 31

What is the correct syntax for declaring an asynchronous function in JavaScript?

Accepted Answer

async functionName() { ... }

Answer

function asyncName() { ... }

Answer

asyncName() { ... }

Answer

function* asyncName() { ... }

Question 32

What is a key advantage of using async/await over callbacks or Promises?

Accepted Answer

Improved code readability and simplified flow control

Answer

Faster execution speed

Answer

Reduced memory usage

Answer

Enhanced security

Question 33

What is the main difference between a callback and a Promise?

Accepted Answer

Promises can be chained, while callbacks cannot

Answer

Callbacks are synchronous, while Promises are asynchronous

Answer

Callbacks can handle multiple asynchronous operations, while Promises can only handle single ones

Answer

Callbacks are more efficient than Promises

Question 34

What is the purpose of the event loop in asynchronous programming?

Accepted Answer

To manage asynchronous tasks and callbacks efficiently in a non-blocking manner

Answer

To execute synchronous code in a single thread

Answer

To store and retrieve data from memory

Answer

To perform complex scientific calculations

Question 35

Which of the following is NOT a way to implement asynchronous programming in JavaScript?

Accepted Answer

Threads

Answer

Callbacks

Answer

Promises

Answer

Async/await

Question 36

What is the purpose of a callback function in asynchronous programming?

Accepted Answer

To handle the result of an asynchronous operation

Answer

To execute a task immediately

Answer

To create a new thread for executing code

Answer

To stop the execution of the program

Question 37

What is the key difference between a callback and a promise?

Accepted Answer

Callbacks can only handle success, while promises can handle both success and failure

Answer

Callbacks are synchronous, while promises are asynchronous

Answer

Promises are synchronous, while callbacks are asynchronous

Answer

Promises can only handle success, while callbacks can handle both success and failure

Question 38

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

Accepted Answer

To create a new asynchronous function

Answer

To mark a function as synchronous

Answer

To handle errors in asynchronous operations

Answer

To stop the execution of the program

Question 39

What is the purpose of the 'await' keyword in asynchronous programming?

Accepted Answer

To pause the execution of the program until a Promise is resolved

Answer

To handle errors in asynchronous operations

Answer

To create a new asynchronous function

Answer

To mark a function as synchronous

Question 40

Which of the following is a best practice for using asynchronous programming?

Accepted Answer

Always use error handling in asynchronous operations.

Answer

Use callbacks whenever possible.

Answer

Avoid using promises.

Answer

Use async/await for even simple asynchronous operations.

Question 41

Which of the following is a key advantage of using asynchronous programming in JavaScript?

Accepted Answer

Improved responsiveness of web applications

Answer

Increased execution speed of synchronous operations

Answer

Simplified code structure

Answer

Reduced memory consumption

Question 42

What is the primary purpose of a callback function in asynchronous programming?

Accepted Answer

To handle the result of an asynchronous operation when it completes

Answer

To initiate the asynchronous operation

Answer

To define the asynchronous operation itself

Question 43

Which of the following is a correct way to handle an error in a Promise?

Accepted Answer

.catch()

Answer

.error()

Answer

.reject()

Answer

.finally()

Question 44

What is a primary benefit of using async/await over Promises?

Accepted Answer

Improved code readability and error handling

Answer

Ability to pause execution of the program

Answer

Faster execution of asynchronous tasks

Question 45

Consider the following code: `async function getData() { const response = await fetch('https://example.com/api/data'); const data = await response.json(); return data; }`. What is the purpose of the `await` keyword in this function?

Accepted Answer

To pause execution until the Promise returned by `fetch()` resolves, then continue with the result

Answer

To handle any errors that may occur during the `fetch()` operation

Answer

To immediately execute the `fetch()` operation

Question 46

What is the primary role of the `async` keyword in JavaScript?

Accepted Answer

To mark a function as asynchronous, indicating that it returns a Promise

Answer

To speed up the execution of the function

Answer

To make the function execute in a separate thread

Answer

To prevent the function from throwing errors

Question 47

Which of these scenarios would NOT benefit from using asynchronous programming?

Accepted Answer

Calculating the factorial of a number

Answer

Fetching data from a remote server

Answer

Handling user input validation

Answer

Loading images for a website

Question 48

What is the difference between `.then()` and `.catch()` in Promises?

Accepted Answer

.then() is for handling successful outcomes, while .catch() is for handling errors or rejections

Answer

.catch() can resolve a Promise

Answer

.then() is executed before .catch()

Question 49

Which of the following is a valid approach to handling asynchronous operations in JavaScript?

Accepted Answer

Using async/await with Promises

Answer

Using Promises without `.then()` or `.catch()`

Answer

Using synchronous functions only

Answer

Implementing callbacks without error handling

Question 50

How do `async` functions interact with Promises?

Accepted Answer

Async functions return Promises, and the `await` keyword pauses execution until the Promise resolves

Answer

Async functions can only be used with Promises that have already resolved

Answer

Async functions automatically resolve Promises without waiting