JavaScript Skills Audio Quiz — Questions & Answers

This quiz contains 10 questions. Below is a complete reference of all questions, answer choices, and correct answers. You can use this section to review after taking the interactive quiz above.

1. Question 1: Promise Polyfill Functionality

   In JavaScript, what is the primary purpose of a Promise polyfill?

   • To provide Promise functionality in environments where Promises are not natively supported
   • To automatically retry asynchronous code on failure
   • To handle CSS animations efficiently
   • To polyfill only arrow functions
   • To add types to all promise-based functions
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   Correct answer: To provide Promise functionality in environments where Promises are not natively supported

2. Question 2: Arrow Function Syntax

   Which one of the following is the correct way to write an arrow function that returns the sum of two numbers 'a' and 'b'?

   • (a, b) => a + b
   • function(a, b) => { return a + b; }
   • [a, b] => { return a + b }
   • a, b -> a + b
   • (a; b) => { return a + b }
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   Correct answer: (a, b) => a + b

3. Question 3: Identifying Closures

   What is a closure in JavaScript?

   • A function having access to its own scope, the outer function's scope, and the global scope
   • A way to close the browser tab automatically
   • A block of code that runs immediately after it is defined
   • An error handling mechanism
   • A pre-compiled JavaScript file
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   Correct answer: A function having access to its own scope, the outer function's scope, and the global scope

4. Question 4: Async and Await

   What does the 'await' keyword do inside an 'async' function in JavaScript?

   • It pauses the execution until the promise is resolved
   • It runs the code synchronously
   • It throws an error if the promise is rejected
   • It creates a new thread
   • It defines a global variable
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   Correct answer: It pauses the execution until the promise is resolved

5. Question 5: LRUCache Implementation

   Which feature does a typical Least Recently Used (LRU) cache provide?

   • Removes the least recently accessed entry when the maximum size is reached
   • Always keeps the oldest entry regardless of access
   • Caches only successful network requests
   • Uses only weak references to stored objects
   • Ignores duplicate cache keys
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   Correct answer: Removes the least recently accessed entry when the maximum size is reached

6. Question 6: Higher-Order Functions

   What is a higher-order function in JavaScript?

   • A function that takes another function as an argument or returns a function
   • A function that always executes asynchronously
   • A function that is hoisted to the top of its scope
   • A function with infinite recursion
   • A function only usable inside classes
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   Correct answer: A function that takes another function as an argument or returns a function

7. Question 7: Object.entries() Usage

   What does Object.entries(obj) return in JavaScript?

   • An array of key-value pairs from the object
   • A list of all values of the object
   • A function reference to the object constructor
   • A sorted array of object keys
   • An iterable of prototype methods
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   Correct answer: An array of key-value pairs from the object

8. Question 8: Identifying Asynchronous Patterns

   Which of the following is NOT a recognized asynchronous programming pattern in JavaScript?

   • Thread locks
   • Promises
   • Callbacks
   • Async functions
   • Event listeners
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   Correct answer: Thread locks

9. Question 9: Code Output: String Manipulation

   Given the code snippet: const result = 'hello'.split('').reverse().join(''); What is the value of 'result'?

   • olleh
   • hello
   • hellohello
   • ehllo
   • heoll
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   Correct answer: olleh

10. Question 10: Dictionary Lookups in JavaScript

    In JavaScript, which approach checks if a string 'word' exists as a key in a given dictionary object called 'dict'?

    • 'word' in dict
    • dict.hasString(word)
    • word == dict.key
    • dict[word] = true;
    • dict.includes(word)
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    Correct answer: 'word' in dict