Basic JavaScript

Question 1

Commenting

Answer 1

Used to leave notes

Code:
// (for single line code)
/* ... */ (for multi-line code)

Question 2

Variables

Answer 2

• Store and manipulate data
• Store different values
• Name to represent data
• Declare a variable

Question 3

Assignment operator

Answer 3

Code:

Stores a value to a variable.

Question 4

Assigning value to another variable

Answer 4

-Use assignment operator

Code:
var a; //no value
a = 7; //has a value
var b; //no value
b = a; //now b = 7

Question 5

Initialize a variable

Answer 5

-Initial value given to a variable

Code:
var a = 9;

Question 6

String literals

Answer 6

• i.e. = string
• Zero or more characters enclosed in single or double quotes

ex: “your name”

Question 7

String variables

Answer 7

A string value assigned to a variable with single or double quotes.

var myFirstName = ‘Lucy’;

Question 8

Uninitialized variables

Answer 8

• Would be ‘undefined’ initially if there is no assigned value.
• In a mathematical operation, the output would be ‘NaN’ (not a number)

Question 9

Case sensitivity

Answer 9

• Use camelCase
• First letter of first word is lowercase and the first letter of all subsequent words are uppercase.

Code:
myFirstName
myLeastFavoriteAnimal

Question 10

Var and let keywords

Answer 10

Var can be overwritten. Could be a problem.

Code:
var camper = 'Fred';
var camper = 'James''
console.log(camper); //James will be printed

Let is better to use. The let variable can only be declared once, if you do not reassign it to a different value.

Question 11

Const

Answer 11

• Read-only
• Cannot be reassigned
• Usually written in all caps with underscore for spacing

Question 12

Number

Answer 12

-Data type which represents numeric data

Question 13

Addition operator

Answer 13

”+”

Question 14

Subtract operator

Answer 14

”-“

Question 15

Multiply operator

Answer 15

“*”

Question 16

Division operator

Answer 16

”/”

Question 17

Increment a number

Answer 17

Code:
i++; (i = i +1)

Adds 1 to a number

Question 18

Decrement a number

Answer 18

Code:

i–; (i = i - 1)

Question 19

Create a decimal number

Answer 19

-Sometimes referred to as floating point numbers or floats

Question 20

Remainder operator

Answer 20

Code:
“%”
const variable = 11 % 3; // Outputs 2

• Gives the remainder of the division of two numbers
• Can be used to check if a number is even or odd

Question 21

Compound assignment (addition)

Answer 21

• (add this to the addition operator card = Everything to the right of the equals sign in evaluated first)
• Does the math operation and assignment in one step.

Code:
“+=”
let myVar = 1;
myVar += 5; // Outputs 6

Question 22

Compound assignment (subtraction)

Answer 22

Code:

“-=”

Question 23

Compound assignment (multiplication)

Answer 23

Code:

“*=”

Question 24

Compound assignment (division)

Answer 24

Code:

“/=”

Question 25

Escaping literal quotes in string

Answer 25

• Use this when you need a quote inside your quote.
• Escape a quote with “"
• Signifies that to JavaScript that it is not the end of the string

Code:
const myStr = "I am a \"double quoted\" string inside \"double quotes\".";