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LearningFuze > JavaScript > Flashcards

JavaScript Flashcards

1
Q

What is the purpose of variables?

A

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

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2
Q

How do you declare a variable?

A

using a keyword like var, const or let

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3
Q

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

A

you assign it a value with the equal operator

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4
Q

What characters are allowed in variable names?

A

$, letters and _underscore not numbers

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5
Q

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

A

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

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6
Q

What is the purpose of a string?

A

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

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7
Q

What is the purpose of a number?

A

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

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8
Q

What is the purpose of a boolean?

A

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

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9
Q

What does the = operator mean in JavaScript?

A

ther assignment operator assigns a value to variable names

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10
Q

How do you update the value of a variable?

A

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

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11
Q

What is the difference between null and undefined?

A

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

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12
Q

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

A

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

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13
Q

Give five examples of JavaScript primitives.

A

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

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14
Q

Difference between primitive and reference data types

A

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

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15
Q

What data type is returned by an arithmetic operation?

A

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

A number

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16
Q

What is string concatenation?

A

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}

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17
Q

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

A

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

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18
Q

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

A

true or false, boolean

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19
Q

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

A

adds a value to the right and updates the variable

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20
Q

What are objects used for?

A

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

grouping variables together

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21
Q

What are object properties?

A

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

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22
Q

Describe object literal notation.

A

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

var keyword var object ope

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23
Q

How do you remove a property from an object?

A

delete operator
delete pet.name

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24
Q

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

A

person.name
person[name]
dot or bracket notation

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25
Q

why use dot versus bracket notation?

A

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

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26
Q

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

A
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27
Q

What are arrays used for?

A

to keep lists of data

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28
Q

Describe array literal notation.

A

variable is assign to the array object

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29
Q

How are arrays different from “plain” objects?

A
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30
Q

What number represents the first index of an array?

A
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31
Q

What is the length property of an array?

A
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32
Q

How do you calculate the last index of an array?

A

the length. -1

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32
Q

How do you calculate the last index of an array?

A

the length. -1

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33
Q

What is a function in JavaScript?

A
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34
Q

Describe the parts of a function definition.

A

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

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35
Q

Describe the parts of a function call.

A

function()
Callingthe function actually performs the specified actions with the indicated parameters. For example, if you define the functionsquare, 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)

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36
Q

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

A

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}

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37
Q

What is the difference between a parameter and an argument?

A

Functionparametersare listed inside the parentheses () in the function definition.
Functionargumentsare thevaluesreceived by the function when it is invoked.
Inside the function, the arguments (the parameters) behave as local variables.

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38
Q

Why are function parameters useful?

A

act as variables and argyu8ments act more like value;

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39
Q

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

A
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40
Q

Why do we log things to the console?

A

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

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41
Q

What is a method?

A

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.

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42
Q

How is a method different from any other function?

A

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

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43
Q

How do you remove the last element from an array?

A

array.pop()

44
Q

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

A

Math.floor

45
Q

How do you generate a random number?

A

Math.floor(Math.random());

46
Q

How do you delete an element from an array?

A

array.splice(start, howMany)

47
Q

How do you append an element to an array?

A

array.push()

48
Q

How do you break a string up into an array?

A

string.split()

49
Q

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

A

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

50
Q

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

A

too many

51
Q

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

A

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

52
Q

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

A

alot

53
Q

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

A

MDN

54
Q

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

A

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.

55
Q

Give 6 examples of comparison operators.

A
56
Q

What data type do comparison expressions evaluate to?

A
57
Q

What is the purpose of an if statement?

A
58
Q

Is else required in order to use an if statement?

A
59
Q

Describe the syntax (structure) of an if statement.

A
60
Q

What are the three logical operators?

A
61
Q

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

A
62
Q

• What is the className property of element objects?

A

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.

63
Q

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

A

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

64
Q

What is the textContent property of element objects?

A

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

gets and sets the node elements

65
Q

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

A

with an assignment operator

66
Q

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

A
67
Q

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

A
68
Q

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

A
69
Q

element.classlist
toggle
remove

A
70
Q

textContent = ‘’; destroys all child elements

A
71
Q

What does the transform property do?

A

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.

72
Q

Give four examples of CSS transform functions.

A

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%);

73
Q

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

A

focus event

74
Q

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

A

blur

75
Q

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

A

input

76
Q

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

A

‘submit’

77
Q

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

A

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

78
Q

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

A

element

79
Q

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

A

name and value
VALUE PROPERTY

80
Q

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

A

waste of time

81
Q

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

A

You see it live and catch mistakes

82
Q

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

A

Orientation
max-width
min-width
height

83
Q

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

A

View port

84
Q

PRINT version is for just printing the text on the page

A
85
Q

What is the event.target?

A

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

86
Q

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

A

because of bubbling?

87
Q

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

A

tagName

88
Q

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

A

the elemnt closest to the event.target

89
Q

How can you remove an element from the DOM?

A

element.remove()

90
Q

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?

A
91
Q

What is the event.target?

A
92
Q

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

A

no display

93
Q

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

A
94
Q

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

A
95
Q

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

A
96
Q

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?

A
97
Q

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?

A
98
Q

What is JSON?

A
99
Q

What are serialization and deserialization?

A
100
Q

Why are serialization and deserialization useful?

A
101
Q

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

A

JSON.stringify

102
Q

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

A

JSON.parse

103
Q

What is JSON

A

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

104
Q

What are serialization and deserialization?

A

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

105
Q

How do you store data in localStorage?

A

localStorage.setItem(‘key’, ‘value’)

106
Q

How do you retrieve data from localStorage?

A

getItem

107
Q

What data type can localStorage save in the browser?

A

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.

108
Q

When does the ‘beforeunload’ event fire on the window object?

A

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

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