Test your skill on map and foreach

If you would like to test your understanding of map and forEach with a few quiz questions, here are few.

Quiz

1. Basic Understanding

Question: What is the primary difference between the map and forEach methods in JavaScript?

a) map modifies the original array, while forEach creates a new array.
b) forEach returns a new array, while map does not return anything.
c) map returns a new array with transformed values, while forEach performs operations without creating a new array.
d) map can only be used on objects, while forEach can be used on arrays.

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2. Practical Application

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

const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map(num => num * 2);
doubled.forEach(num => console.log(num));

a) 1, 2, 3, 4, 5
b) 2, 4, 6, 8, 10
c) [2, 4, 6, 8, 10]
d) 2 2 4 4 6 6 8 8 10 10

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3. Side Effects

Question: Which method would you use if you need to perform an operation that doesn’t require the creation of a new array, such as logging each element to the console?

a) map
b) forEach
c) Both map and forEach
d) Neither map nor forEach

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4. Performance

Question: If you are concerned about performance and need to perform an operation on each array element without creating a new array, which method is generally more efficient?

a) map
b) forEach
c) Both are equally efficient
d) It depends on the size of the array

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5. Coding Challenge

Question: Consider the following code snippet. What will be the output of the agesNextYear variable?

const users = [
  { name: 'Alice', age: 12 },
  { name: 'Bob', age: 18 },
  { name: 'Charlie', age: 20 }
];

const agesNextYear = users.map(user => user.age + 1);
console.log(agesNextYear);

a) [12, 18, 20]
b) [13, 19, 21]
c) [13, 18, 21]
d) [12, 19, 20]

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6. Use Case

Question: Which method is better suited for transforming each element of an array and generating a new array from these transformations?

a) map
b) forEach
c) filter
d) reduce

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Answers

1. c) map returns a new array with transformed values, while forEach performs operations without creating a new array.
2. b) 2, 4, 6, 8, 10
3. b) forEach
4. b) forEach
5. b) [13, 19, 21]
6. a) map

How did you do? Let me know if you’d like explanations for any of the answers or if you have more questions!