JavaScript

Question 1

What is the purpose of variables?

Answer 1

tto tem,porarily store information for the computer to use in order to get the desired result

Question 2

How do you declare a variable?

Answer 2

using a keyword like var, const or let

Question 3

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

Answer 3

you assign it a value with the equal operator

Question 4

What characters are allowed in variable names?

Answer 4

$, letters and _underscore not numbers

Question 5

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

Answer 5

it means, the the same word written with different cases are two different variables

Question 6

What is the purpose of a string?

Answer 6

holds words, inside quotation marks, can add written information for user, works with any kind of text

Question 7

What is the purpose of a number?

Answer 7

to allow the computer to calculate as well as moving elements on a page, holds numeric value;

Question 8

What is the purpose of a boolean?

Answer 8

to give the computer true or false data, it helps ‘check’ things, allows for true or false

Question 9

What does the = operator mean in JavaScript?

Answer 9

ther assignment operator assigns a value to variable names

Question 10

How do you update the value of a variable?

Answer 10

you do not have to declare it again, you just use the assignment operator

Question 11

What is the difference between null and undefined?

Answer 11

undefined is the immediate value of a variable if it hasn’t been assigned a value or for formal arguments where there are nno actual arguments

In computer science, a null value represents a reference that points, generally intentionally, to a nonexistent or invalid object or address. The meaning of a null reference varies among language implementations.
null can also be used for a place to store a value to be changed later

Question 12

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

Answer 12

so that you keep track of your consoles
tells you what line number you’re on

Question 13

Give five examples of JavaScript primitives.

Answer 13

null, undefined, string data, numeric data, boolean data

Question 14

Difference between primitive and reference data types

Answer 14

primitives stores the variable in memory location
reference stores the address of where the information is

Question 15

What data type is returned by an arithmetic operation?

Answer 15

Arithmetic operators take numerical values (either literals or variables) as their operands and return a single numerical value.

A number

Question 16

What is string concatenation?

Answer 16

Concatenate just means “join together”. To join together strings in JavaScript you can use a different type of string, called a template literal.

‘string’ + ‘string’
${string}

Question 17

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

Answer 17

addition of number values, and string concatenation
+ operator if it receives two numbers it knows it needs to add,
if it receives a string, it knows to concantenate

Question 18

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

Answer 18

true or false, boolean

Question 19

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

Answer 19

adds a value to the right and updates the variable

Question 20

What are objects used for?

Answer 20

objects group together a set of variables and functions that create a model of something that exists in the real world

grouping variables together

Question 21

What are object properties?

Answer 21

in an object, variables are known as properties - they can hold information like the name of a hotel
name: ‘Hilton’ -> that is the property

Question 22

Describe object literal notation.

Answer 22

var object = { name(key): louisa(value) }
key value pairs

var keyword var object ope

Question 23

How do you remove a property from an object?

Answer 23

delete operator
delete pet.name

Question 24

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

Answer 24

person.name
person[name]
dot or bracket notation

Question 25

why use dot versus bracket notation?

Answer 25

bracket notation allows us to use a variable to store a property name student.name can only be name var prop = 'color' vehicle[prop] = 'white' ^^ bracket is substition bracket also allows to accessor create an illegal variable names look at pictures

Question 26

Objects are addresses, they point to the first point of data you're storing a reference to a memory base that points to the first value reference data point

Question 27

What are arrays used for?

Answer 27

to keep lists of data

Question 28

Describe array literal notation.

Answer 28

variable is assign to the array object

Question 29

How are arrays different from "plain" objects?

Question 30

What number represents the first index of an array?

Question 31

What is the length property of an array?

Question 32

How do you calculate the last index of an array?

Answer 32

the length. -1

Question 32

How do you calculate the last index of an array?

Answer 32

the length. -1

Question 33

What is a function in JavaScript?

Question 34

Describe the parts of a function definition.

Answer 34

function ex(hi, yo) { var ex = y return x}

Question 35

Describe the parts of a function call.

Answer 35

function() Calling the function actually performs the specified actions with the indicated parameters. For example, if you define the function square, you could call it as follows: code inside the function will execute when "something" invokes (calls) the function: When an event occurs (when a user clicks a button) When it is invoked (called) from JavaScript code Automatically (self invoked)

Question 36

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

Answer 36

Once defined, a function is just another kind of object. However, it is special in that it can be called. A function must be called for the code within its code block to run. option key word Parameter { code black}

Question 37

What is the difference between a parameter and an argument?

Answer 37

Function parameters are listed inside the parentheses () in the function definition. Function arguments are the values received by the function when it is invoked. Inside the function, the arguments (the parameters) behave as local variables.

Question 38

Why are function parameters useful?

Answer 38

act as variables and argyu8ments act more like value;

Question 39

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

Question 40

Why do we log things to the console?

Answer 40

The JavaScript console is a debugging tool. It is where the browser prints errors and warnings as they occur in your JavaScript code.

Question 41

What is a method?

Answer 41

A method is a function which is a property of an object. Random is the function - the value is what the function does There are two kinds of methods: instance methods which are built-in tasks performed by an object instance, or static methods which are tasks that are called directly on an object constructor.

Question 42

How is a method different from any other function?

Answer 42

In JavaScript functions themselves are objects, so, in that context, a method is actually an object reference to a function. Other than being a property of an object, difference is only that the method is assignedf to a property

Question 43

How do you remove the last element from an array?

Answer 43

array.pop()

Question 44

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

Answer 44

Math.floor

Question 45

How do you generate a random number?

Answer 45

Math.floor(Math.random());

Question 46

How do you delete an element from an array?

Answer 46

array.splice(start, howMany)

Question 47

How do you append an element to an array?

Answer 47

array.push()

Question 48

How do you break a string up into an array?

Answer 48

string.split()

Question 49

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

Answer 49

No, but you can assign the modified string to a new variable MDN or console.log

Question 50

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

Answer 50

too many

Question 51

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

Answer 51

if you don't need the return value of something, the return value isnt useful, for instance splice

Question 52

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

Answer 52

alot

Question 53

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

Answer 53

MDN

Question 54

Math.max(1, 2, 3) - is 3

Answer 54

The Math.max() function returns the largest of the zero or more numbers given as input parameters, or NaN if any parameter isn't a number and can't be converted into one.

Question 55

Give 6 examples of comparison operators.

Question 56

What data type do comparison expressions evaluate to?

Question 57

What is the purpose of an if statement?

Question 58

Is else required in order to use an if statement?

Question 59

Describe the syntax (structure) of an if statement.

Question 60

What are the three logical operators?

Question 61

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

Question 62

• What is the className property of element objects?

Answer 62

The className property of the Element interface gets and sets the value of the class attribute of the specified element. A string variable representing the class or space-separated classes of the current element.

Question 63

How do you update the CSS class attribute of an element using JavaScript?

Answer 63

query the element and add the property on the variable that is queryselected, you need to use = sign

Question 64

What is the textContent property of element objects?

Answer 64

The textContent property of the Node interface represents the text content of the node and its descendants. gets and sets the node elements

Question 65

How do you update the text within an element using JavaScript?

Answer 65

with an assignment operator

Question 66

Is the event parameter of an event listener callback always useful?

Question 67

Would this assignment be simpler or more complicated if we didn't use a variable to keep track of the number of clicks?

Question 68

Would this assignment be simpler or more complicated if we didn't use a variable to keep track of the number of clicks?

Question 69

element.classlist toggle remove

Question 70

textContent = ''; destroys all child elements

Question 71

What does the transform property do?

Answer 71

The transform CSS property lets you rotate, scale, skew, or translate an element. It modifies the coordinate space of the CSS visual formatting model. If the property has a value different than none, a stacking context will be created. In that case, the element will act as a containing block for any position: fixed; or position: absolute; elements that it contains.

Question 72

Give four examples of CSS transform functions.

Answer 72

transform: matrix(1, 2, 3, 4, 5, 6); transform: translate(120px, 50%); transform: scale(2, 0.5); transform: skew(30deg, 20deg); transform: scale(0.5) translate(-100%, -100%);

Question 73

What event is fired when a user places their cursor in a form control?

Answer 73

focus event

Question 74

What event is fired when a user's cursor leaves a form control?

Answer 74

blur

Question 75

What event is fired as a user changes the value of a form control?

Answer 75

input

Question 76

What event is fired when a user clicks the "submit" button within a form?

Answer 76

'submit'

Question 77

What does the event.preventDefault() method do? What does submitting a form without event.preventDefault() do?

Answer 77

stops page from refreshing, submit forms by default refresh and lose inouts

Question 78

What property of a form element object contains all of the form's controls.

Answer 78

element

Question 79

What property of a form control object gets and sets its value?

Answer 79

name and value VALUE PROPERTY

Question 80

What is one risk of writing a lot of code without checking to see if it works so far?

Answer 80

waste of time

Question 81

What is an advantage of having your console open when writing a JavaScript program?

Answer 81

You see it live and catch mistakes

Question 82

Give two examples of media features that you can query in an @media rule.

Answer 82

Orientation max-width min-width height

Question 83

Which HTML meta tag is used in mobile-responsive web pages?

Answer 83

View port

Question 84

PRINT version is for just printing the text on the page

Question 85

What is the event.target?

Answer 85

The read-only target property of the Event interface is a reference to the object onto which the event was dispatched. The event.target property can be used in order to implement event delegation. The actual thing that is clicked

Question 86

Why is it possible to listen for events on one element that actually happen its descendent elements?

Answer 86

because of bubbling?

Question 87

What DOM element property tells you what type of element it is?

Answer 87

tagName

Question 88

What does the element.closest() method take as its argument and what does it return?

Answer 88

the elemnt closest to the event.target

Question 89

How can you remove an element from the DOM?

Answer 89

element.remove()

Question 90

If you wanted to insert new clickable DOM elements into the page using JavaScript, how could you avoid adding an event listener to every new element individually?

Question 91

What is the event.target?

Question 92

What is the affect of setting an element to display: none?

Answer 92

no display

Question 93

What does the element.matches() method take as an argument and what does it return?

Question 94

How can you retrieve the value of an element's attribute?

Question 95

At what steps of the solution would it be helpful to log things to the console?

Question 96

If you were to add another tab and view to your HTML, but you didn't use event delegation, how would your JavaScript code be written instead?

Question 97

If you didn't use a loop to conditionally show or hide the views in the page, how would your JavaScript code be written instead?

Question 98

What is JSON?

Question 99

What are serialization and deserialization?

Question 100

Why are serialization and deserialization useful?

Question 101

How do you serialize a data structure into a JSON string using JavaScript?

Answer 101

JSON.stringify

Question 102

How do you deserialize a JSON string into a data structure using JavaScript?

Answer 102

JSON.parse

Question 103

What is JSON

Answer 103

avaScript Object Notation (JSON) is a standard text-based format for representing structured data based on JavaScript object syntax

Question 104

What are serialization and deserialization?

Answer 104

Serialization is the process of turning an object in memory into a stream of bytes so you can do stuff like store it on disk or send it over the network. breakes into bytes

Question 105

How do you store data in localStorage?

Answer 105

localStorage.setItem('key', 'value')

Question 106

How do you retrieve data from localStorage?

Answer 106

getItem

Question 107

What data type can localStorage save in the browser?

Answer 107

keyName A string containing the name of the key you want to create/update. keyValue A string containing the value you want to give the key you are creating/updating.

Question 108

When does the 'beforeunload' event fire on the window object?

Answer 108

Does whatever it needs to do before the page refreshes or changes