Javascript

Question 1

Variable

Answer 1

“name storage” for data. Use ‘let’ to create a variable in Javascript. Variable is right after.

Question 2

Show 2 variables coping data.

Answer 2

let hello = ‘hello world!’;
let message;

message = hello world;

Question 3

How many times should a variable be declared ?

Answer 3

Once

Question 4

Variable Limitations

Answer 4

1. Name MUST contain letters, numbers or symbols $ and _

2. First character must not be a digit

Question 5

Valid Variable Names

Answer 5

1. let userName;
2. let test123;
3. let $;
   4 let _;

Question 6

Does case matter ?

Answer 6

YES!!

apple and AppLE are two different variables.

Question 7

Reserved names

Answer 7

let
class 
return
function

Question 8

Use strict

Answer 8

Allow you not to use ‘let’, as long as you define to use strict.
Must put: “use strict”;

Question 9

Constants

Answer 9

Declare a constant(UNCHANGING) variable, uses ‘const’ instead of ‘let’

Question 10

Can ‘const’ be reassigned ?

Answer 10

NO!

Question 11

Uppercase constants

Answer 11

used for difficult to remember values that are known prior to execution

Question 12

When do you use uppercase constants?

Answer 12

When variable values never change. Ex. color codes, birthdays etc.

Question 13

Infinity

Answer 13

is a special value that is greater than any number.

• alert (1/0);
• alert(Infinity);

Question 14

How many special numeric values are there ?

Answer 14

3. Infinity, -Infinity and NaN

Question 15

NaN

Answer 15

represent a computational error. It is a result of a incorrect or undefined math operation

Question 16

Number Data Type

Answer 16

Cant present integer values larger than 2(53_1) superscript or less than -(253-1) for neg.

Question 17

BigInt

Answer 17

represent integers of arbitrary length.appending n to the end of an integer:
const bigInt = 1234567890123456789012345678901234567890n;

Question 18

How many quotes are there in Javascript?

Answer 18

3. • Double “Hello”
   • Single ‘Hello’
   • BackticksHello

Question 19

Backticks

Answer 19

“extended functionality” quotes. They allow us to embed variables and expressions into a string by wrapping them in ${…}

Ex:let name = “John”;

// embed a variable
alert( `Hello, ${name}!` ); // Hello, John!

// embed an expression
alert( `the result is ${1 + 2}` ); // the result is

Question 20

Boolean

Answer 20

has only two values: true and false.

This type is commonly used to store yes/no values: true means “yes, correct”, and false means “no, incorrect”.

Question 21

Null

Answer 21

null is not a “reference to a non-existing object” or a “null pointer” like in some other languages.

It’s just a special value which represents “nothing”, “empty” or “value unknown”.

Question 22

Undefined

Question 23

Undefined

Answer 23

“value is not assigned”.

If a variable is declared, but not assigned, then its value is undefined:

let age;

alert(age); // shows “undefined”

Question 24

Object

Question 24

Object

Answer 24

objects are used to store collections of data and more complex entities.

Question 25

Symbol

Answer 25

used to create unique identifiers for objects.

Question 26

Typeof operator

Answer 26

returns the type of the argument. It’s useful when we want to process values of different types differently or just want to do a quick check.

typeof undefined // “undefined”

typeof 0 // “number”

typeof 10n // “bigint”

typeof true // “boolean”

typeof “foo” // “string”

typeof Symbol(“id”) // “symbol”

Question 27

How many data types are there in Javascript?

Answer 27

8

• number
• bigint
• string
• boolean
• null
• undefined
• object
• symbol