Test your skill on Advanced JavaScript

1. Basic Understanding

Question: What is the primary purpose of the map method in JavaScript?

a) To filter elements based on a condition
b) To aggregate elements into a single value
c) To create a new array by applying a function to each element of the original array
d) To execute a function on each element without returning a new array

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2. Practical Application

Question: Given the following code, what will be the output of squaredNumbers?

const numbers = [2, 4, 6];
const squaredNumbers = numbers.map(num => num * num);
console.log(squaredNumbers);

a) [2, 4, 6]
b) [4, 16, 36]
c) [4, 8, 12]
d) [8, 16, 24]

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3. Filtering Data

Question: How does the filter method determine which elements to include in the new array?

a) It maps each element to a new value
b) It accumulates elements into a single value
c) It selects elements based on whether they pass a specified test function
d) It flattens nested arrays

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4. Aggregating Data

Question: What does the following code snippet do?

const numbers = [1, 2, 3, 4, 5];
const product = numbers.reduce((acc, num) => acc * num, 1);
console.log(product);

a) Calculates the sum of the numbers
b) Calculates the product of the numbers
c) Finds the maximum number
d) Finds the average of the numbers

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5. Combining Methods

Question: What is the result of the following code?

const items = [
  { name: 'Pen', quantity: 10 },
  { name: 'Notebook', quantity: 5 },
  { name: 'Eraser', quantity: 8 }
];

const itemDescriptions = items
  .filter(item => item.quantity > 5)
  .map(item => `${item.name} (Quantity: ${item.quantity})`);

console.log(itemDescriptions);

a) [‘Pen (Quantity: 10)’, ‘Notebook (Quantity: 5)’, ‘Eraser (Quantity: 8)’]
b) [‘Pen (Quantity: 10)’, ‘Eraser (Quantity: 8)’]
c) [‘Pen’, ‘Eraser’]
d) [‘Notebook (Quantity: 5)’]

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6. Using flatMap

Question: What will be the output of the following code?

const phrases = [
  'Learn JavaScript',
  'Transform Data'
];

const words = phrases.flatMap(phrase => phrase.split(' '));
console.log(words);

a) [‘Learn’, ‘JavaScript’, ‘Transform’, ‘Data’]
b) [‘Learn JavaScript’, ‘Transform Data’]
c) [‘Learn’, ‘JavaScript’]
d) [‘Transform’, ‘Data’]

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Answers

1. c) To create a new array by applying a function to each element of the original array
2. b) [4, 16, 36]
3. c) It selects elements based on whether they pass a specified test function
4. b) Calculates the product of the numbers
5. b) [‘Pen (Quantity: 10)’, ‘Eraser (Quantity: 8)’]
6. a) [‘Learn’, ‘JavaScript’, ‘Transform’, ‘Data’]

How did you do? Let me know if you’d like explanations for any of the answers or if you need further practice!