Array Accessors and Mutators

Question 1

Access (index into) an Array item (index lookup)

Answer 1

array[0]

Question 2

Add to the end of an Array

Answer 2

array.push()

Question 3

Remove from the end of an Array

Answer 3

array.pop()

Question 4

Add element to the front of an Array

Answer 4

array.unshift(element)

Question 5

Remove from the front of an Array

Answer 5

array.shift()

Question 6

Find the index of an item in the Array

Answer 6

array.indexOf(‘item’)

Question 7

Remove an item by index position, mutates original array.

Answer 7

array.splice(pos, deleteCount, item) (mutable)
let array = [1,2,3]

array. splice(1, 0, 3) // [1,3,2,3]
array. splice(1, 1, 3) // [1,3,3]

Question 8

Copy section of an Array

Answer 8

array.slice(start, end) (immutable - shallow copy)

let array = ['cat', 'dog', 'mouse']
array. slice(1) // ['dog', 'mouse']
array. slice(0,2) // ['cat', 'dog']

Question 9

Convert the Array to a String

Answer 9

array.toString() [1, 2, ‘a’, ‘1a’] -> “1,2,a,1a”

Question 10

Check for a specific value

Answer 10

array.includes()

Question 11

Convert to separated String

Answer 11

array.join()
[‘Fire’, ‘Air’, ‘Water’] .join() -> “Fire,Air,Water”
.join(‘-‘) -> “Fire-Air-Water”

Question 12

Populate all elements of an array to a static value

Answer 12

array.fill()

Array(3).fill({}) // [{}, {}, {}]

Question 13

Merge two or more arrays into a new array (immutable)

Answer 13

array.concat() or spread [...array1, ...array2]
const array1 = ['a', 'b', 'c'];
const array2 = ['d', 'e', 'f'];
const array3 = array1.concat(array2); // ["a", "b", "c", "d", "e", "f"]

Question 14

Merge two arrays into an existing array (mutable)

Answer 14

existingArray.push.apply(existingArray, newArray)

let existingArray = [1,2,3]

let newArray = [4,5,6]

existingArray.push.apply(existingArray, newArray) // [1,2,3,4,5,6]

Question 15

Combine nested arrays into single flattend array

Answer 15

array.flat() (immutable - returns new array)

Question 16

Create an array of all of the indexes of an array

Answer 16

array.keys()

Question 17

Create and return a new string by concatenating all of the elements in this array,

Answer 17

array.join()

const elements = [“Fire”, “Air”, “Water”];
elements.join(“-“); // Expected output: “Fire-Air-Water”

Question 18

Returns the last index at which a given element can be found in the array,

Answer 18

const animals = [“Dodo”, “Tiger”, “Penguin”, “Dodo”];

animals.lastIndexOf(‘Dodo’) // 3

Question 19

Reverse an array in place, returns a reference to the original array

Answer 19

array.reverse()

Question 20

Removes the first element of an array and returns that element

Answer 20

array.shift()

Question 21

Sorts an array in place, returns a reference to the original array

Answer 21

array.sort()

Question 22

Returns an iterator with the values of given array

Answer 22

array.values()

Question 23

Replace a value with the given index. Returns a new array

Answer 23

array.with()

Question 24

Returns a string representing the elements of an array using Locale

Answer 24

array.toLocaleString()

const array1 = [1, "a", new Date("21 Dec 1997 14:12:00 UTC")];
const localeString = array1.toLocaleString("en", { timeZone: "America/New_York" });