Vanilla JS

Question 1

How do you create Undefined?

Answer 1

let firstName;

console.log(firstName);

Question 2

What does typeof operator do?

Answer 2

console. log(typeof ‘Iman Sayah’) // string
console. log(typeof 5) // number
console. log(typeof true) // boolean
console. log(typeof null) // object type
console. log(typeof undefined) // undefined

Question 3

Primitive data types are immutable? Example?

Answer 3

let word = "JavaScript"
word[0] = "K"
// error

Question 4

What are primitive data types in JavaScript?

Answer 4

Numbers - Integers, floats
Strings - Any data under single quote, double quote or backtick quote
Booleans - true or false value
Null - empty value or no value
Undefined - a declared variable without a value

Question 5

What are non-primitive data type in JavaScript?

Answer 5

Objects
Functions
Arrays

Question 6

Which data types are immutable?

a) primitive
b) non-primitive

Answer 6

primitive

Question 7

How do you create a random number between 0 and 0.999999?

Answer 7

Math.random()

Question 8

Math.round()
Math.floor()
Math.ceil()
Math.min()
Math.max()

Answer 8

round to nearest int
round down to nearset int
round up to nearest int
min of a list of values: Math.min(1,2,3)
max of a list of values: Math.max(1,2,3)

Question 9

How do you generate a number between 0 and 10?

Answer 9

let randomNum = Math.random()                     // generates 0 to 0.999
let numBtnZeroAndTen = randomNum * 11     // this gives: min 0 and max 10.99
let randomNumRoundToFloor = Math.floor(numBtnZeroAndTen)

// Shortened
let randNum = Math.floor(Math.random() * 10 + 1)

Question 10

Which method is preferred for concatenating two strings?
A - Using “+”
B - Using ``

Answer 10

B - Back-ticks

console.log(The sum of ${a} and ${b} is ${a + b})

Question 11

.length

Answer 11

length of string

Question 12

.toUpperCase()

Answer 12

all capital letters

Question 13

.toLowerCase()

Answer 13

all lower case letters

Question 14

.substr(start, count)

Answer 14

start from starting index and return n characters.

DEPRECATED!!!

Question 15

.substring(start, end)

.substring(start)

Answer 15

The substring() method returns the part of the string between the start and end indexes, or to the end of the string.

Question 16

.split(by, count)

Answer 16

cuts out the string by substring and return n chunks

Question 17

What is the output of
let myName = “Iman Sayah”
console.log(myName.split(‘a’));

Answer 17

[ ‘Im’, ‘n S’, ‘y’, ‘h’ ]

Question 18

What is the output of
let myName = “Iman Sayah”
console.log(myName.split(‘a’, 2));

Answer 18

[ ‘Im’, ‘n S’ ]

Question 19

What is the output of
let myName = “Iman Sayah”
console.log(myName.split(‘’));

Answer 19

[
‘I’, ‘m’, ‘a’, ‘n’, ‘ ‘, ‘S’, ‘a’, ‘y’, ‘a’, ‘h’
]

Question 20

What is the output of
let myName = “Iman Sayah”
console.log(myName.split(‘ ‘));

Answer 20

[ ‘Iman’, ‘Sayah’ ]

Question 21

What is the output of
let myName = “Iman Sayah”
console.log(myName.split(‘X’));

Answer 21

[ ‘Iman Sayah’ ]

Question 22

.trim()

Answer 22

Removes the leading and trailing white space and line terminator characters from a string.

Question 23

.includes(substring)

Answer 23

checks if substring argument exists in the string

Question 24

.replace(substring, new)

Answer 24

replaces substring with new substring

Question 25

.charAt(index)

Answer 25

returns a new string consisting of the single UTF-16 code unit located at the specified offset into the string.

Question 26

What is the output of
“iman”.charAt(4)
?

Answer 26

””

Question 27

What is the output of
“iman”.charAt(3)
?

Answer 27

“n”

Question 28

What is the result of
“iman”.charCodeAt(3)
?

Answer 28

110

Question 29

What is the result of
“iman”.charCodeAt(5)
?

Answer 29

NaN

Question 30

.charCodeAt()

Answer 30

returns an integer between 0 and 65535 representing the UTF-16 code unit at the given index.

returns NaN when index is out of range.

Question 31

.indexOf()

Answer 31

returns the first index at which a given element can be found in the array, or -1 if it is not present.

Question 32

What is the result of

“iman sayah”.indexOf(“a”)

Answer 32

2

Question 33

What is the result of

“iman sayah”.indexOf(“t”)

Answer 33

-1