Javascript Array Methods

Question 1

concat()

Answer 1

Joins arrays and returns an array with the joined arrays

let arrayOne = [“apples”, “oranges”];
let arrayTwo = [“grapes”, “strawberries”];
Let answer = arrayOne.concat(arrayTwo);
console.log(answer)

OUTPUT:
apples, oranges, grapes, strawberries

Question 2

copyWithin()

Answer 2

Copies array elements within the array, to and from specified positions

array.copyWithin(target, start, end)

let fruit = [“soccer”, “football”, “basketball”, “baseball”, “tennis”];
let arrOne = fruit.copyWithin(1,3);
console.log(arrOne);

OUTPUT:
[“soccer”, “baseball”, “tennis”, “baseball”, “tennis”]

Question 3

entries()

Answer 3

Returns a key/value pair Array Iteration Object

array.entries()

let sports = [“soccer”, “football”, “basketball”, “baseball”];
let answer = sports.entries();
console.log(answer.next().value);
console.log(answer.next().value);

OUTPUT:
[0, “soccer”]
[1, “football”]

Question 4

every()

Answer 4

Checks if every element in an array pass a test

let scores = [95, 50, 75, 100, 80, 45]
const passed = (current) => current > 50
console.log(scores.every(passed));

OUTPUT:
false

Question 5

fill()

Answer 5

Fill the elements in an array with with a static value

array.fill(value, start, end)

let sports = [“soccer”, “football”, “basketball”, “baseball”];
let answer = sports.fill(“soccer”);
console.log(answer)

OUTPUT:
[“soccer”, “soccer”, “soccer”, “soccer”]
——————————————————-

let sports = [“soccer”, “football”, “basketball”, “baseball”];
let answer = sports.fill(“soccer”, 2, 4);
console.log(answer)

OUTPUT:
[“soccer”, “football”, “soccer”, “soccer”]

Question 6

filter()

Answer 6

Creates a new array with every element in an array that pass a test

array.filter(function(currentValue, index, arr), thisValue)

let scores = [95, 97, 35, 47, 85]
let pass = scores.filter(checkScore);

function checkScore(scores) {
return scores > 50;
}

OUTPUT:
[95, 97, 85]

Question 7

find()

Answer 7

Returns the value of the first element in an array that pass a test

array.find(function(currentValue, index, arr),thisValue)

let scores = [95, 77, 50, 85, 100, 97]
let found = scores.find(a => a > 90)
console.log(found)

OUTPUT:
95

Question 8

findIndex()

Answer 8

Returns the index of the first element in an array that pass a test. If none pass the test then -1 is returned

let scores = [20, 55, 35, 75, 85]
let pass = scores.findIndex(a => a > 70)
console.log(pass)

OUTPUT:
3

Question 9

forEach()

Answer 9

Calls a function for each array element

array.forEach(function(currentValue, index, arr), thisValue)

let arrOne = [“apple”, “orange”, “banana”]
arrOne.forEach(a => console.log(a));

OUTPUT:
“apple”
“orange”
“banana”

Question 10

from()

Answer 10

Creates an array from an object

Array.from(object, mapFunction, thisValue)

console.log(Array.from(‘soccer’));

OUTPUT:
[“s”, “o”, “c”, “c”, “e”, “r”]

Question 11

includes()

Answer 11

Check if an array contains the specified element

let numbers = [1, 2, 3, 7, 9];
let answer = numbers.includes(9);
console.log(answer);

OUTPUT:
true

Question 12

indexOf()

Answer 12

Search the array for an element and returns its position

string.indexOf(searchvalue, start)

let sports = [“soccer”, “football”, “basketball”, “baseball”, “soccer”];

let answer = sports.indexOf(“soccer”);
console.log(answer);

OUTPUT:
0

————————————————

let sports = [“soccer”, “football”, “basketball”, “baseball”, “soccer”];

let answer = sports.indexOf(“soccer”, 1);
console.log(answer);

OUTPUT:
4

Question 13

isArray()

Answer 13

Checks whether an object is an array

Array.isArray(value)

let numbers = [2, 5, 7, 9]
let answer = Array.isArray(numbers)
console.log(answer)

OUTPUT:
true

Question 14

join()

Answer 14

Joins all elements of an array into a string

Question 15

keys()

Answer 15

Returns an Array Iteration object, containing the keys of the original array

Question 16

lastIndexOf()

Answer 16

Search the array for an element, starting at the end, and returns it’s position

Question 17

length

Answer 17

Sets or returns the number of elements in an array

Question 18

map()

Answer 18

Creates a new array with the result of calling a function for each array element

Question 19

pop()

Answer 19

Removes the last element of an array, and returns that element

Question 20

push()

Answer 20

Adds new elements to the end of an array, and returns the new length

Question 21

reduce()

Answer 21

Reduce the values of an array to a single value (going left to right)

Question 22

reduceRight()

Answer 22

Reduce the values of an array to a single value (going right-to-left)

Question 23

reverse()

Answer 23

Reverse the order of the elements in an array

Question 24

shift()

Answer 24

Removes the first element of an array, and returns that element

Question 25

slice()

Answer 25

Selects a part of an array, and returns the new array

const animals = [‘soccer’, ‘football’, ‘baseball’, ‘tennis’]

console.log(animals.slice(2));

Output:
[‘baseball’, ‘tennis’]

Question 26

some()

Answer 26

Checks if any of the elements in an array pass a test

Question 27

sort()

Answer 27

Sorts the element of an array

Question 28

splice()

Answer 28

Adds/removes elements from an array

Question 29

toString()

Answer 29

Converts an array to a string, and returns the result

Question 30

unshift()

Answer 30

Adds new elements to the beginning of an array, and returns the new length

Question 31

valueOf()

Answer 31

Returns the primitive value of an array