JavaScript Array Methods

Question 1

What does `Array.prototype.map()` return?

Accepted Answer

A new array with each element transformed by the callback

Answer

The original array modified in place

Answer

A boolean indicating whether all elements passed a test

Answer

The first element that satisfies a condition

Question 2

What does `Array.prototype.reduce()` do?

Accepted Answer

Applies a function against an accumulator and each element to reduce the array to a single value

Answer

Removes duplicate values from an array

Answer

Splits an array into chunks

Answer

Converts an array to an object

Question 3

What is the difference between `Array.prototype.find()` and `Array.prototype.filter()`?

Accepted Answer

`find()` returns the first matching element; `filter()` returns an array of all matches

Answer

`find()` returns all matches; `filter()` returns the first match

Answer

They are identical

Answer

`find()` searches by index; `filter()` searches by value

Question 4

What does `Array.prototype.flat()` do?

Accepted Answer

Creates a new array with sub-arrays concatenated into it up to a specified depth

Answer

Sorts the array in ascending order

Answer

Converts the array to a flat string

Answer

Removes falsy values from the array

Question 5

What does `Array.prototype.some()` return?

Accepted Answer

true if at least one element passes the test, otherwise false

Answer

The first element that passes the test

Answer

An array of elements that pass the test

Answer

The number of elements that pass the test

Question 6

How does `Array.prototype.splice()` differ from `Array.prototype.slice()`?

Accepted Answer

`splice()` modifies the original array; `slice()` returns a new sub-array without modifying the original

Answer

They are identical methods with different names

Answer

`slice()` modifies the original; `splice()` does not

Answer

`splice()` only removes elements; `slice()` only adds elements