JavaScript Foundations

Question 1

What is the purpose of variables?

Answer 1

To store values

Question 2

How do you declare a variable?

Answer 2

‘var varName’

Question 3

How do you initialize (assign a value to) a variable?

Answer 3

var varName = ‘assignedValue’

Question 4

What characters are allowed in variable names?

Answer 4

letters, _, $

And after first letter: numbers, letters, _, $

Question 5

What does it mean to say that variable names are “case sensitive”?

Answer 5

var varName is different from var varname

Question 6

What is the purpose of a string?

Answer 6

To store a value that contains any characters

Question 7

What is the purpose of a number?

Answer 7

Used to manipulate numbers/do math

Question 8

What is the purpose of a boolean?

Answer 8

Create logic in a JavaScript file. Sets up true/false values

Question 9

What does the = operator mean in JavaScript?

Answer 9

It is used as a way to assign values to variables

Question 10

How do you update the value of a variable?

Answer 10

Either declare it again or edit the value where the variable was declared earlier

Question 11

What is the difference between null and undefined?

Answer 11

Null means it is defined but intentionally missing a value

Undefined means it isn’t defined and it doesn’t exist

Question 12

Why is it a good habit to include “labels” when you log values to the browser console?

Answer 12

For readability/communication for those reading the code

Question 13

Give five examples of JavaScript primitives.

Answer 13

Undefined
Null
Boolean
String
Number

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Number

Question 15

What is string concatenation?

Answer 15

‘string’+’string’ which combines the strings together

Question 16

What purpose(s) does the + plus operator serve in JavaScript?

Answer 16

It concatenates values

Question 17

What data type is returned by comparing two values (<, >, ===, etc)?

Answer 17

Boolean

Question 18

What are objects used for?

Answer 18

To store data/values that are bigger than if you just stored it into one variable

Question 19

What are object properties?

Answer 19

The defining characteristics of an object

Question 20

Describe object literal notation.

Answer 20

const objectName = { property1: key1, property2: key2,… etc } ;

Question 21

How do you remove a property from an object?

Answer 21

Use the delete operator

Example:
delete objectName.property1

Question 22

What are the two ways to get or update the value of a property?

Answer 22

Using dot notation:
objectName.propertyName or objectName.propertyName = newValue

Using bracket notation:
objectName[‘propertyName’] or objectName[‘propertyName’] = newValue

Question 23

What are arrays used for?

Answer 23

Stores a list of values

Question 24

Describe array literal notation.

Answer 24

const arrayName = [ value1, value2,… etc ];

Question 25

How are arrays different from “plain” objects?

Answer 25

An array is a list of values assigned to a variable

An object is a list of properties assigned to a variable

Question 26

What number represents the first index of an array?

Answer 26

0

Question 27

What is the length property of an array?

Answer 27

Lists how long the array is

Question 28

How do you calculate the last index of an array?