Arrays

Question 1

How is an array declared?

Answer 1

let arr = []

Question 2

What method is used to append an element to the end of an array?

Answer 2

.push(value)

Question 3

What method is used to remove an element from the end of an array?

Answer 3

.pop()

Question 4

How do you return an element from a specific index?

Answer 4

arr.at(index)

Question 5

How do you set an element at a specific index?

Answer 5

arr[index] = value;

Question 6

How do you convert an array to a string of comma separated values?

Answer 6

array.toString()

Question 7

How do you remove the first element from an array?

Answer 7

shift()
This method removes the first element from an array and returns that removed element. It changes the length of the array.

Question 8

How do you add one or more elements to the beginning of an array?

Answer 8

unshift(…items) -
Adds one or more elements to the beginning of an array and returns the new length of the array.

Question 9

How do you remove an element from an array at a specific index without changing the length of the array?

Answer 9

delete arr[index] - Removes an element at the specified index. This operation leaves a hole (undefined element) in the array and does not change the array’s length.

Question 10

How do you merge two or more arrays into a new array?

Answer 10

arr.concat(…values) - Merges two or more arrays or values into a new array without modifying the original arrays.

Question 11

How do you create a new array with all sub-array elements concatenated into it recursively up to a specified depth?

Answer 11

arr.flat(depth) - Creates a new array with all sub-array elements concatenated into it up to the specified depth. The default depth is 1.

Question 12

How do you change the contents of an array by removing or replacing existing elements and/or adding new elements?

Answer 12

arr.splice(start, deleteCount, …items) - Changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.

Question 13

How do you return a shallow copy of a portion of an array into a new array object in JavaScript?

Answer 13

let new_arr = arr.slice(start,end) - Returns a shallow copy of a portion of an array into a new array object. It selects from start to end (end not included). The original array is not modified.

Question 14

How do you find the first index of a specified element in an array?

Answer 14

indexOf(searchElement, fromIndex) - Returns the first index at which a given element can be found in the array, or -1 if it is not present. The search starts from fromIndex if provided.

Question 15

How do you find the last index of a specified element in an array?

Answer 15

lastIndexOf(searchElement, fromIndex) - Returns the last index at which a given element can be found in the array, or -1 if it is not present. The search starts backward from fromIndex.

Question 16

How do you determine whether an array includes a certain value?

Answer 16

includes(searchElement, fromIndex) - Determines whether the array includes a certain value, returning true or false. The search starts from fromIndex if provided.

Question 17

How do you find the first element in an array that satisfies a provided testing function?

Answer 17

arr.find - Returns the value of the first element in the array that satisfies the provided testing function. Otherwise, it returns undefined.

Question 18

How do you find the index of the first element in an array that satisfies a provided testing function?

Answer 18

findIndex(testFunction, thisArg) - Returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1.

Question 19

How do you find the last element in an array that satisfies a provided testing function?

Answer 19

findLast(testFunction, thisArg) - Returns the value of the last element in the array that satisfies the provided testing function. If no elements satisfy the testing function, undefined is returned.

Question 20

How do you find the index of the last element in an array that satisfies a provided testing function?

Answer 20

findLastIndex(testFunction, thisArg) - Returns the index of the last element in the array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.