Map method in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the map() method do in JavaScript?

The map() method creates a new array by applying a function to each element of the original array.

beginner

How does map() differ from forEach()?

map() returns a new array with transformed elements, while forEach() just runs a function on each element without returning anything.

intermediate

What arguments does the callback function inside map() receive?

The callback receives three arguments: the current element, the index of the element, and the original array.

intermediate

Can map() change the size of the array it returns?

No, map() always returns a new array of the same length as the original array.

beginner

Give an example of using map() to double numbers in an array.

Example: <br><code>const numbers = [1, 2, 3];<br>const doubled = numbers.map(n => n * 2);<br>console.log(doubled); // [2, 4, 6]</code>

What does the map() method return?

A A single value

B Undefined

C The original array

D A new array with transformed elements

map() always returns a new array where each element is the result of the callback function.

Which of these is a valid use of map()?

A To filter out elements from an array

B To create a new array by modifying each element

C To sort an array

D To remove duplicates

map() transforms each element and returns a new array of the same length.

What arguments does the callback function in map() receive?

A Element, index, array

B Element only

C Index only

D Array only

The callback receives the current element, its index, and the original array.

If you want to change the size of an array, is map() the right method?

A No, it keeps the same length

B Yes, but only to add elements

C Yes, it can add or remove elements

D No, it deletes elements only

map() always returns an array with the same number of elements as the original.

What will this code output? <br>[1, 2, 3].map(x => x + 1)

A [1, 3, 5]

B [1, 2, 3]

C [2, 3, 4]

D [0, 1, 2]

Each element is increased by 1, so the new array is [2, 3, 4].

Explain how the map() method works and when you would use it.

Think about turning a list of raw items into a list of changed items.

Describe the difference between map() and forEach() in JavaScript.

One returns a new list, the other just runs code on each item.