JavaScript Concepts

Question 1

What data type is returned by an arithmetic operation?

Answer 1

Number

Question 2

What is string concatenation?

Answer 2

its when you combine strings using the + operator

Question 3

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

Answer 3

for numbers, it acts as the addition operator. 2+ 3 = 5

for strings, it acts as a concatenator

Question 4

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

Answer 4

boolean, either true or false

Question 5

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

Answer 5

it is a shortcut command.

if word += 5 is the same as word = word + 5

Question 6

What is the purpose of variables?

Answer 6

to assign a value for later reference. var area = 3 * 2

Question 7

How do you declare a variable?

Answer 7

by using the keywords var , let , const

Question 8

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

Answer 8

by using the = sign

Question 9

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

Answer 9

if the cases in the variable name are not matched exactly, an error will show

Question 10

What does the = operator mean in JavaScript?

Answer 10

it is used to set values of variables

Question 11

How do you update the value of a variable?

Answer 11

by using the variable name then the equal sign, followed by new value

Question 12

What are objects used for?

Answer 12

a collection of properties where those properties can have their own values

Question 13

What are object properties?

Answer 13

they are variable names that are attached to the object and they can have their values. The values can be different types but the properties are strings.

Question 14

Describe object literal notation.

Answer 14

var obj = {
}

Question 15

How do you remove a property from an object?

Answer 15

delete nameOfObject.PropertyToDelete

Question 16

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

Answer 16

dot notation or bracket notation

Question 17

What data type is returned by an arithmetic operation?

Answer 17

Numbers, including NaN since its type is number

Question 18

What is string concatenation?

Answer 18

when you condense 2 or more strings into 1 string using the + operator

Question 19

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

Answer 19

for strings it will be used to concatenate
for numbers it is used to add
for string + number it will concatenate by turning the number into a string

Question 20

What is a function in JavaScript?

Answer 20

a formula, can be customized by you to take 0, 1, or more arguments. It will return a value., if you do not use return it will return undefined

Question 21

Describe the parts of a function definition.

Answer 21

function key word, function name, parenthesis, and parameters (optional)

Question 22

Describe the parts of a function call.

Answer 22

function name followed by (arguments here)
example.  greet('tom')

Question 23

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

Answer 23

function definition is just the code that you wrote, it will not run until it is called with ()

Question 24

What is the difference between a parameter and an argument?

Answer 24

parameters are used when a function is declared. argument are the values that are passed into the parameters when the function is called

Question 25

Why are function parameters useful?

Answer 25

you can use them as variables, which gives way more flexibility to do stuff

Question 26

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

Answer 26

1) it ENDS the function when the JS engine finishes the return statement line 2) it returns a value from the function

Question 27

What are arrays used for?

Answer 27

to have a collection of data by an ordered list, starting at index 0

Question 28

Describe array literal notation

Answer 28

var = [] empty brackets mean array literal

Question 29

How are arrays different from "plain" objects?

Answer 29

arrays do NOT have a property name and value. They have an index and a value. But like object, the value can be any type aka functions, objects, another array, number, string, etc

Question 30

What number represents the first index of an array?

Answer 30

0

Question 31

What is the length property of an array?

Answer 31

how many items it contains = the length

Question 32

How do you calculate the last index of an array?

Answer 32

by using arrayName.length - 1

Question 33

Why do we log things to the console?

Answer 33

to check our work during development phase

Question 34

What is a method?

Answer 34

a function attached to an object as a property

Question 35

How is a method different from any other function?

Answer 35

you must call it by calling the object first, using dot notation

Question 36

How do you remove the last element from an array?

Answer 36

the pop method

Question 37

How do you round a number down to the nearest integer?

Answer 37

use Math.floor(number here)

Question 38

How do you generate a random number?

Answer 38

Math.random(numbers here) it is only from 0-.999999999999999999999

Question 39

How do you delete an element from an array?

Answer 39

use the splice method, it is the 2nd argument

Question 40

How do you append an element to an array?

Answer 40

by using splice or push

Question 41

How do you break a string up into an array?

Answer 41

the split method

Question 42

Do string methods change the original string? How would you check if you weren't sure?

Answer 42

no they do not, you can console.log the original variable assigned the the original string to check

Question 43

Roughly how many string methods are there according to the MDN Web docs?

Answer 43

40

Question 44

Is the return value of a function or method useful in every situation?

Answer 44

most of the time yes

Question 45

Roughly how many array methods are there according to the MDN Web docs?

Answer 45

about 35

Question 46

What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?

Answer 46

MDN

Question 47

Give 6 examples of comparison operators.

Answer 47

``` < > == === > = < = ```

Question 48

What data type do comparison expressions evaluate to?

Answer 48

boolean so either true or false

Question 49

What is the purpose of an if statement?

Answer 49

to check conditions

Question 50

Is else required in order to use an if statement?

Answer 50

no

Question 51

Describe the syntax (structure) of an if statement.

Answer 51

if ( condition here ) { code here }

Question 52

What are the three logical operators?

Answer 52

&& (and) || (or) ! (not)

Question 53

How do you compare two different expressions in the same condition?

Answer 53

use either && or ||

Question 54

What is the purpose of a loop?

Answer 54

to check values of collection 1 by 1, you can do something during those checks

Question 55

What is the purpose of a condition expression in a loop?

Answer 55

the parameters for when the loop stops/runs

Question 56

What does "iteration" mean in the context of loops?

Answer 56

cycling through each element/value

Question 57

When does the condition expression of a while loop get evaluated?

Answer 57

at the start of the loop

Question 58

When does the initialization expression of a for loop get evaluated?

Answer 58

at the start of the loop

Question 59

When does the condition expression of a for loop get evaluated

Answer 59

after initialization

Question 60

When does the final expression of a for loop get evaluated?

Answer 60

after the condition has ran

Question 61

Besides a return statement, which exits its entire function block, which keyword exits a loop before its condition expression evaluates to false?

Answer 61

break

Question 62

What does the ++ increment operator do?

Answer 62

increases the value of the variable attached by 1

Question 63

How do you iterate through the keys of an object?

Answer 63

by using the for in loop

Question 64

What is a method?

Answer 64

a function inside an obj

Question 65

How can you tell the difference between a method definition and a method call?

Answer 65

definition is when it is being defined inside the function. A method call is requires dot notation to access the method inside the function

Question 66

Describe method definition syntax (structure).

Answer 66

propertyName : function name( parameters) { code block }

Question 67

Describe method call syntax (structure).

Answer 67

objName.Propertyname.methodName( )

Question 68

How is a method different from any other function?

Answer 68

it is part of an object

Question 69

What is the defining characteristic of Object-Oriented Programming?

Answer 69

writing procedural functions and storing them inside objects, which can then be accessed via dot notation

Question 70

What are the four "principles" of Object-Oriented Programming?

Answer 70

Abstraction Encapsulation Inheritance Polymorphism

Question 71

What is "abstraction"?

Answer 71

being able to work with (possibly) complex things in simple ways

Question 72

What does API stand for?

Answer 72

Application Programming Interface

Question 73

What is the purpose of an API?

Answer 73

is a set of functions that allows applications to access data and interact with external software components, operating systems, or microservices