JavaScript

Question 1

What is the purpose of variables?

Answer 1

to hold data (numbers, strings, booleans)

Question 2

How do you declare a variable?

Answer 2

by creating a variable name

Question 3

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

Answer 3

adding an equal sign next the variable name and then giving it a value/data

Question 4

What characters are allowed in variable names?

Answer 4

letters, $, numbers but we shouldn’t use numbers

Question 5

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

Answer 5

it means that the capitalization needs to be the same in order to call that variable (ex. var myName and var MyName is two different variables)

Question 6

What is the purpose of a string?

Answer 6

it holds the data type of letters and other characters

Question 7

What is the purpose of a number?

Answer 7

it holds the data type of numbers (integers, decimals, etc)

Question 8

What is the purpose of a boolean?

Answer 8

it holds the data type of one of two values, true or false

Question 9

What does the = operator mean in JavaScript?

Answer 9

a value is being assigned to a variable

Question 10

How do you update the value of a variable?

Answer 10

by assigning it to a new value

Question 11

What is the difference between null and undefined?

Answer 11

null is subject to change, there is nothing but it could change into something. while undefined is literally nothing

Question 12

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

Answer 12

so that you won’t get confused to what is being logged

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, number, boolean, null, undefined

Question 14

What data type is returned by an arithmetic operation?

Answer 14

a number

Question 15

What is string concatenation?

Answer 15

when two or more strings are added together

Question 16

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

Answer 16

used to add one value to another

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

it adds and re-assigns a new value to a variable

Question 19

What are objects used for?

Answer 19

to hold a set of variables that all link to one thing/object

Question 20

What are object properties?

Answer 20

it tells us about the object, stores info ab the object (ex. name:, age:,)

Question 21

Describe object literal notation.

Answer 21

an array of keys and values

Question 22

How do you remove a property from an object?

Answer 22

using the delete operator

Question 23

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

Answer 23

using a dot notation or bracket notation (ex. example.name, example[‘name’])

Question 24

What are arrays used for?

Answer 24

to store multiple values

Question 25

Describe array literal notation.

Answer 25

values within brackets [ ] (ex. var colors = ['red', 'white', 'blue']

Question 26

How are arrays different from "plain" objects?

Answer 26

arrays store actual variables in an index starting from 0

Question 27

What number represents the first index of an array?

Answer 27

0

Question 28

What is the length property of an array?

Answer 28

it shows the amount of variables inside of an array

Question 29

How do you calculate the last index of an array?

Answer 29

by subtracting the length of an array by 1 (ex. var lastIndex = example.length -1;)

Question 30

What is a function in JavaScript?

Answer 30

it is a "power" tool, it is used to run a sequence of code when it is called

Question 31

Describe the parts of a function definition.

Answer 31

a function definition is the name used for that function so you have something to call it, also contains parameters (ex. function sayHello(name) {} )

Question 32

Describe the parts of a function call.

Answer 32

you can call a function using the function definition and parenthesis (ex. sayHello('Tim') )

Question 33

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

Answer 33

function call has the value inside(a parameter) the parenthesis while the function definition has a variable (argument) inside

Question 34

What is the difference between a parameter and an argument?

Answer 34

a parameter is like a placeholder for the value like a variable, an argument has a value. when we define a function we declare a parameter, when we call a function we pass it arguments

Question 35

Why are function parameters useful?

Answer 35

it's a placeholder so that we know what will come out as an argument

Question 36

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

Answer 36

it produces a value for us to use and it prevents any more code in the function's code block to run

Question 37

Why do we log things to the console?

Answer 37

so that we able to see what the code is producing

Question 38

What is a method?

Answer 38

it is a function which is a property of an object

Question 39

How is a method different from any other function?

Answer 39

methods are associated with objects while function just performs a task when called

Question 40

How do you remove the last element from an array?

Answer 40

using the pop() method

Question 41

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

Answer 41

using the Math.floor() method

Question 42

How do you generate a random number?

Answer 42

using the Math.random() method

Question 43

How do you delete an element from an array?

Answer 43

using the slice() , pop(), shift() method

Question 44

How do you append an element to an array?

Answer 44

using the push() method

Question 45

How do you break a string up into an array?

Answer 45

using the split() method

Question 46

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

Answer 46

string methods doesn't change the original string. to double check you can log it to the console

Question 47

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

Answer 47

about 50

Question 48

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

Answer 48

no

Question 49

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

Answer 49

about 40

Question 50

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

Answer 50

mdn

Question 51

Give 6 examples of comparison operators.

Answer 51

!=, ===, <, >, <=, >=, !==

Question 52

What data type do comparison expressions evaluate to?

Answer 52

boolean

Question 53

What is the purpose of an if statement?

Answer 53

so that the code will only run if the requirements are met

Question 54

Is else required in order to use an if statement?

Answer 54

no

Question 55

Describe the syntax (structure) of an if statement.

Answer 55

if (x = y) { return 'yay; }

Question 56

What are the three logical operators?

Answer 56

&&, ||, !

Question 57

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

Answer 57

by using a logical operator && or | |

Question 58

What is the purpose of a loop?

Answer 58

to run code over and over until the outcome is false or when it is capped

Question 59

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

Answer 59

to see if the expression is true or not so it knows when to stop

Question 60

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

Answer 60

a sequence of code run repeatidly

Question 61

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

Answer 61

after the initialization expression

Question 62

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

Answer 62

after the incrementation in the final expression or at the beginning of the iteration if it is the first time

Question 63

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

Answer 63

before starting a new iteration

Question 64

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

Answer 64

after the iteration of the loop

Question 65

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

Answer 65

break;

Question 66

What does the ++ increment operator do?

Answer 66

goes up 1

Question 67

How do you iterate through the keys of an object?

Answer 67

using for in loops

Question 68

Why do we log things to the console?

Answer 68

it is a debugger, it helps inspect a certain element

Question 69

What is a "model"?

Answer 69

a model is the looks and design of a document that is being put on a page from memory. models are made with objects

Question 70

Which "document" is being referred to in the phrase Document Object Model?

Answer 70

the document that is in the script element

Question 71

What is the word "object" referring to in the phrase Document Object Model?

Answer 71

the nodes

Question 72

What is a DOM Tree?

Answer 72

a dom tree consists of multiple nodes each representing an text content, elements, attributes, etc.

Question 73

Give two examples of document methods that retrieve a single element from the DOM.

Answer 73

document.querySelector() document.getElementById()

Question 74

Give one example of a document method that retrieves multiple elements from the DOM at once.

Answer 74

document.querySelectorAll()

Question 75

Why might you want to assign the return value of a DOM query to a variable?

Answer 75

it is easier to console log and console dir

Question 76

What console method allows you to inspect the properties of a DOM element object?

Answer 76

console.dir()

Question 77

Why would a