(Full Stack JavaScript) Asynchronous Code Knowledge Assessment Guide 2024, Exams of Javascript programming

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FULL STACK JAVASCRIPT

Asynchronous Code

KNOWLEDGE ASSESSMENT GUIDE

1. Which of the following is true about Promises in JavaScript?
   • A) Promises are used to handle synchronous operations.
   • B) Promises can be in one of three states: pending, fulfilled, or rejected.
   • C) Promises are a replacement for callbacks.
   • D) Promises are used to handle synchronous and asynchronous operations. Answer: B Rationale: Promises are used to handle asynchronous operations and can be in one of three states: pending, fulfilled, or rejected.
2. What does the async keyword do when added to a function?
   • A) It makes the function run synchronously.
   • B) It makes the function return a Promise.
   • C) It makes the function run faster.
   • D) It makes the function return a callback. Answer: B Rationale: The async keyword makes a function return a Promise, allowing the use of await within the function.

• B) Fulfilled
• C) Rejected
• D) Completed Answer: D Rationale: The states of a JavaScript Promise are pending, fulfilled, and rejected.

Fill-in-the-Blank Questions

6. In JavaScript, the __________ method is used to execute a function after a specified delay. Answer: setTimeout Rationale: The setTimeout method is used to execute a function after a specified delay.
7. The __________ method is used to repeatedly execute a function at specified intervals. Answer: setInterval Rationale: The setInterval method is used to repeatedly execute a function at specified intervals.

8. The __________ function is used to create a new Promise. Answer: Promise Rationale: The Promise function is used to create a new Promise.
9. In an async function, the __________ keyword is used to wait for a Promise to resolve. Answer: await Rationale: The await keyword is used to wait for a Promise to resolve in an async function.
10. The __________ method is used to handle the final state of a Promise, regardless of its outcome. Answer: finally Rationale: The finally method is used to handle the final state of a Promise, regardless of its outcome.

True/False Questions

11. True or False: The async keyword can only be used with functions that return a Promise.

15. True or False: The Promise.race() method waits for the first Promise to resolve or reject. Answer: True Rationale: The Promise.race() method waits for the first Promise to resolve or reject.

Multiple Choice Questions (Continued)

16. Which of the following is a correct way to create a new Promise?
    • A) new Promise(resolve, reject)
    • B) new Promise((resolve, reject) => {})
    • C) Promise.create((resolve, reject) => {})
    • D) Promise.new((resolve, reject) => {}) Answer: B Rationale: The correct way to create a new Promise is new Promise((resolve, reject) => {}).
17. What does the Promise.resolve() method do?
    • A) It creates a new Promise that is already resolved.
    • B) It creates a new Promise that is pending.
    • C) It creates a new Promise that is rejected.

• D) It creates a new Promise that is fulfilled. Answer: A Rationale: The Promise.resolve() method creates a new Promise that is already resolved.

18. Which of the following is true about the Promise.allSettled() method?

• A) It waits for all Promises to resolve.
• B) It waits for all Promises to settle (resolve or reject).
• C) It waits for the first Promise to resolve.
• D) It waits for the first Promise to settle (resolve or reject). Answer: B Rationale: The Promise.allSettled() method waits for all Promises to settle (resolve or reject).

19. What is the purpose of the Promise.reject() method?

• A) To create a new Promise that is already resolved.
• B) To create a new Promise that is pending.
• C) To create a new Promise that is rejected.
• D) To create a new Promise that is fulfilled.

Fill-in-the-Blank: Callback functions are commonly used in JavaScript to handle _ operations. Correct Answer: asynchronous Rationale: Callback functions are frequently used in JavaScript to manage asynchronous operations, ensuring that certain tasks are executed after others have completed. True/False: Asynchronous code in JavaScript always runs in parallel with synchronous code. Correct Answer: False Rationale: Asynchronous code in JavaScript does not always run in parallel with synchronous code; it allows certain tasks to be executed independently of the main program flow. Multiple Choice: Which function is used to handle errors in asynchronous JavaScript code? A) errorHandler() B) catch() C) tryCatch() D) handleError() Correct Answer: B) catch()

Rationale: The catch() method is used to handle errors in asynchronous JavaScript code, allowing developers to manage and respond to exceptions that occur during asynchronous operations. Fill-in-the-Blank: Promises in JavaScript are used to represent the eventual completion (or failure) of an _ operation. Correct Answer: asynchronous Rationale: Promises in JavaScript are a mechanism for handling asynchronous operations, providing a way to work with asynchronous code in a more organized and manageable manner. True/False: The async keyword in JavaScript is used to define a function that executes synchronously. Correct Answer: False Rationale: The async keyword in JavaScript is used to define a function that returns a promise, allowing the function to execute asynchronously. Multiple Choice: Which method is used to run multiple asynchronous operations concurrently in JavaScript? A) parallel() B) all() C) together()

A) resolve B) then C) complete D) finish Correct Answer: B) then Rationale: The then keyword in JavaScript is used to handle promises and specify the actions to take when a promise is resolved. Fill-in-the-Blank: The async/await syntax in JavaScript provides a more _ way of working with promises. Correct Answer: synchronous Rationale: The async/await syntax allows developers to write asynchronous code in a more synchronous and readable manner, simplifying the handling of promises. True/False: JavaScript's event loop is responsible for managing asynchronous operations and callbacks. Correct Answer: True Rationale: The event loop in JavaScript is a key mechanism for managing asynchronous operations, ensuring that callback functions are executed at the appropriate times. Multiple Choice:

Which function is used to reject a promise in JavaScript? A) reject() B) fail() C) error() D) catch() Correct Answer: A) reject() Rationale: The reject() function is used to reject a promise in JavaScript, indicating that the promised task has failed or encountered an error. Fill-in-the-Blank: The Promise.race() method in JavaScript resolves or rejects a set of promises as soon as the _ promise is resolved or rejected. Correct Answer: first Rationale: The Promise.race() method in JavaScript operates on a set of promises and resolves or rejects them based on the first promise that is resolved or rejected. True/False: Asynchronous code in JavaScript can lead to callback hell, making code difficult to read and maintain. Correct Answer: True Rationale: Asynchronous code in JavaScript, if not properly structured, can lead to callback hell - a situation where nested callbacks make code hard to read and maintain.

Rationale: The setTimeout() function in JavaScript is an asynchronous operation that schedules a function to run after a specified amount of time, allowing the code to continue executing without waiting for the delay to finish. Multiple Choice: Which method is used to convert a callback-based function to a promise- based function in JavaScript? A) toPromise() B) promisify() C) callbackToPromise() D) convert() Correct Answer: B) promisify() Rationale: The promisify() method in JavaScript is commonly used to convert callback-based functions into promise-based functions, simplifying the handling of asynchronous operations. Fill-in-the-Blank: JavaScript's async/await syntax is built on top of _ and provides a more intuitive way of working with promises. Correct Answer: promises Rationale: The async/await syntax in JavaScript builds upon promises and offers developers a more intuitive and synchronous way of interacting with asynchronous code, enhancing readability and maintainability.

1. Multiple Choice: Which of the following statements best describes asynchronous code in JavaScript? A) Allows tasks to execute alongside other tasks without waiting for them to finish B) Ensures tasks are executed in a sequential manner C) Always results in faster execution times compared to synchronous code D) Is only useful for simple operations Correct Answer: A Rationale: Asynchronous code allows tasks to run concurrently without waiting for each other to finish.
2. Fill in the Blank: To handle asynchronous operations in JavaScript, developers commonly use ________ to manage callbacks and promises. Correct Answer: Promises Rationale: Promises are commonly used in JavaScript to handle asynchronous operations and avoid callback hell.
3. True/False: Event listeners in JavaScript are an example of asynchronous code execution. Correct Answer: True

Correct Answer: True Rationale: Asynchronous code execution helps prevent blocking operations, enhancing the responsiveness of web applications.

7. Multiple Choice: Which method is typically used to perform asynchronous operations in Node.js? A) setTimeout B) setInterval C) readFile D) console.log Correct Answer: C Rationale: The readFile method in Node.js is commonly used for asynchronous file operations.
8. Fill in the Blank: Callback functions in JavaScript are commonly used to handle the ________ of asynchronous operations. Correct Answer: Results Rationale: Callback functions are often used to process or handle the results of asynchronous operations.
9. True/False: Asynchronous code execution in JavaScript can prevent the main thread from being blocked while waiting for time-consuming tasks to complete.

Correct Answer: True Rationale: Asynchronous code execution allows the main thread to continue executing other tasks while waiting for asynchronous operations to complete.

10. Multiple Choice: Which method is used to handle errors in a chain of promises in JavaScript? A) .done() B) .finally() C) .catch() D) .fail() Correct Answer: C Rationale: The .catch() method is used to handle errors in a chain of promises in JavaScript.
11. Fill in the Blank: The async/await syntax in JavaScript provides a more ________ way to write asynchronous code compared to using promises. Correct Answer: Synchronous Rationale: async/await syntax allows developers to write asynchronous code that looks synchronous, improving readability.