JavaScript Backend

Question 1

Read a JSON file

Answer 1

fetch(‘path/to/JSON.json’)
.then(res => res.json())
.then(data => {
console.log(data);
})
.catch(err => console.error(‘Error’: err));

Question 2

Add to end of array

Answer 2

arr.push(4)

Question 3

Remove starting element from array

Answer 3

arr.shift()

Question 4

Remove last element in array

Answer 4

arr.pop()

Question 5

Remove element/s in middle of array

Answer 5

arr.splice(1, 2)

Question 6

Add element/s to middle of array

Answer 6

arr.splice(1, 0, 2, 3) //adds 2, 3 at index 1

Question 7

Convert string to array

Answer 7

arr.split(‘’)

Question 8

Extract substring

Answer 8

str.slice(0, 5)

Question 9

Convert string to upper case

Answer 9

str.toUpperCase()

Question 10

Convert string to lower case

Answer 10

str.toLowerCase

Question 11

Does string include value

Answer 11

str.includes(‘a’)

Question 12

Does a certain key exist in object

Answer 12

obj.hasOwnProperty(‘a’)
‘a’ in obj

Question 13

Add key value pair to object

Answer 13

obj[‘c’] = 3

Question 14

Get array of keys from object

Answer 14

Object.keys(obj)

Question 15

Delete key value pair

Answer 15

delete obj.a

Question 16

Loop through keys in an object

Answer 16

for (let key in obj) {
}

Question 17

Initiate a set

Answer 17

mySet = new Set()
= new Set([1, 2, 3])

Question 18

Add value to set

Answer 18

mySet.add(4)

Question 19

How to see if value in set

Answer 19

mySet.has(3)

Question 20

Delete value from set

Answer 20

mySet.delete(2)

Question 21

Remove duplicates from an array

Answer 21

let newArr = [… new Set(array)]

Question 22

Find length of set

Answer 22

mySet.size()

Question 23

Iterate over values in a set

Answer 23

for (let value of mySet) {
}

Question 24

Clear set

Answer 24

mySet.clear()

Question 25

Create a map

Answer 25

let myMap = new Map()

Question 26

Add to a map

Answer 26

myMap.set(‘a’, 1)

Question 27

Get a value with key

Answer 27

myMap.get(‘a’)

Question 28

Does key exist in map

Answer 28

myMap.has(‘b’)

Question 29

Delete key value pair from map

Answer 29

myMap.delete(‘a’)

Question 30

Round down number

Answer 30

Math.floor(4.8) // 4

Question 31

Round up number

Answer 31

Math.ceil(4.2) // 5

Question 32

Find remainder of division

Answer 32

10 % 3 // 1

Question 33

Sort elements in place

Answer 33

arr.sort((a, b) => a -b)

Question 34

Pass filter on array

Answer 34

arr.filter(num => num > 2)

Question 35

Pass function on every element in array and return array

Answer 35

arr.map(num => num * 2)

Question 36

Execute function on each array element

Answer 36

arr.forEach(num => console.log(num))

Question 37

Write a normal function

Answer 37

function greet() {
console.log(‘Hello World’)
}

Question 38

Write an arrow function

Answer 38

let greet = () => {
console.log(‘Hello World’)
}

Question 39

Find character at index for string

Answer 39

str.charAt(7)

Question 40

Find index of substring in string

Answer 40

str.indexOf(‘World’)

Question 41

Replace substring with other string

Answer 41

str.replace(‘World’, ‘Universe’)