JavaScript

Question 1

What is the purpose of variables?

Answer 1

to store data that we can access later

Question 2

How do you declare a variable?

Answer 2

variable key word with variable name, var keyword

Question 3

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

Answer 3

Assign a value after the assignment operator

var keyword name of variable = value

Question 4

What characters are allowed in variable names?

Answer 4

letters, numbers, dollar sign $, or underscore _

Question 5

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

Answer 5

the same word lowercase and uppercase would be different variable names

Question 6

What is the purpose of a string?

Answer 6

to add new content into a page
store date with text content
save a series of characters

Question 7

What is the purpose of a number?

Answer 7

stores numeric value

count, math financial stuff, measurement of some sort

Question 8

What is the purpose of a boolean?

Answer 8

data type two possible values
yes or no

make decisions
do or don’t do

Question 9

What does the = operator mean in JavaScript?

Answer 9

assignment operator

assign value to variable

Question 10

How do you update the value of a variable?

Answer 10

reassigning it without declaring it again, without the variable keyword

var unknown = null; first time only one
unknown = 4 reassigning

Question 11

What is the difference between null and undefined?

Answer 11

null is intentional -assigned as a value, do it on purpose

undefined no value hasn’t been assigned yet -nothing, empty

Question 12

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

Answer 12

to help you debug

Always put a label

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, number, boolean, undefined, and null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

number

Question 15

What is string concatenation?

Answer 15

combine two strings or more to create one new string

Question 16

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

Answer 16

adds one value to another or concatenation

used to join the strings on either side of it

Question 17

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

Answer 17

boolean

Question 18

What does the += “plus-equals” operator do?

Answer 18

addition assignment, adds the values on both left and right operands

Question 19

What are objects used for?

Answer 19

to group together a set of variables and functions to represent something such as a person or a car

store data together, collection of stuff

Question 20

What are object properties?

Answer 20

variable within an object

Question 21

Describe object literal notation.

Answer 21

properties of the object are stored within curly braces

Question 22

How do you remove a property from an object?

Answer 22

delete object.property

Question 23

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

Answer 23

dot notation and bracket notation

Question 24

What are arrays used for?

Answer 24

it stores a list of values

Question 25

Describe array literal notation.

Answer 25

the values are assigned to the array inside a pair of square brackets, and each values separated by a comma

var = [ ]

Question 26

How are arrays different from “plain” objects?

Answer 26

The key for the value of an array is a number. The number is the location in the array.

number indexes

Question 27

What number represents the first index of an array?

Answer 27

zero [0]

Question 28

What is the length property of an array?

Answer 28

holds the number of items in the array

Question 29

How do you calculate the last index of an array?

Answer 29

array.length - 1

Question 30

What is a function in JavaScript?

Answer 30

packages of code that can be called later in the program

Question 31

Describe the parts of a function definition.

Answer 31

the function keyword
an optional name
zero or more parameters
a code block
an optional return statement

Question 32

Describe the parts of a function call.

Answer 32

the function name followed by the arguments replacing the parameters in ( )

Question 33

When comparing them side-by-side, what are the differences between a function call and a function definition?

Answer 33

function call passes an argument

function definition is a set of instructions

Question 34

What is the difference between a parameter and an argument?

Answer 34

parameter-placeholder

arguments-value to fill placeholder

Question 35

Why are function parameters useful?

Answer 35

pass additional info into the function

Question 36

What two effects does a return statement have on the behavior of a function?

Answer 36

causes a function to produce a value

prevents any more code in the functions code block from being run