Javascript

Question 1

What is the purpose of variables?

Answer 1

to store data for the future.

Question 2

How do you declare a variable?

Answer 2

utilizing the var keyword to declare it.

Question 3

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

Answer 3

You assign the variable name (identifier) to a value using a single = sign.

Question 4

What characters are allowed in variable names?

Answer 4

letters, underscore, start with $ or underscore camelCased capitalized letters but numbers cant be in the front.

Question 5

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

Answer 5

that the same variable name but with different casing have different variable names.

Question 6

What is the purpose of a string?

Answer 6

how to hold a sequence of data characters of characters of numbers letters and other characters

Question 7

What is the purpose of a number?

Answer 7

to store number mainly for math

Question 8

What is the purpose of a boolean?

Answer 8

to compare expressions as true or false.

Question 9

What does the = operator mean in JavaScript?

Answer 9

assignment operator.

Question 10

How do you update the value of a variable?

Answer 10

you set the variable name without the keyword to another variable value

Question 11

What is the difference between null and undefined?

Answer 11

null is the intentional absence of value where it is an object. it can be assigned but not output by java. but undefined does not have a value assigned to a variable. 1) null get data later or it was never going to be added and you will know. Java outputs undefined so developers should not.

Question 12

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

Answer 12

logging the value without the label makes it unknown what it is being used and where it comes from.

Question 13

Give five examples of JavaScript primitives.

Answer 13

str, num, undefined, boolean, null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

numbers

Question 15

What is string concatenation?

Answer 15

when you combine strings utilizing , or + as any other data type becomes a string

Question 16

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

Answer 16

Addition or concatenation

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 sets the value of the left side as it self plus what is on the right side

Question 19

What are objects used for?

Answer 19

objects group together different variables datatypes can group multiple properties in association of the same object as well as being able have multiple similar object with differing properties be better organized.

Question 20

What are object properties?

Answer 20

piece of data stored in object. easiest method to notate objects with curly brackets being assigned to a variable. with key vales.

Question 21

Describe object literal notation.

Answer 21

defining the object and assigning to a curly brackets with a property key name : value

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

through appending or using the = operator to the property and giving a value.

Question 24

Give 6 examples of comparison operators.

Answer 24

> =
<=
<
===
!=

Question 25

What data type do comparison expressions evaluate to?

Answer 25

boolean

Question 26

What is the purpose of an if statement?

Answer 26

to compare in a conditional.

Question 27

Is else required in order to use an if statement?

Answer 27

no

Question 28

Describe the syntax (structure) of an if statement.

Answer 28

if condition {conditional block}

Question 29

What are the three logical operators?

Answer 29

&& and || or ! not

Question 30

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

Answer 30

using logical operators

Question 31

Why do we log things to the console?

Answer 31

for debugging or to better understand how a process works.

Question 32

What is a method?

Answer 32

it is a function within an object

Question 33

How is a method different from any other function?

Answer 33

its is held within an object

Question 34

How do you remove the last element from an array?

Answer 34

array.pop

Question 35

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

Answer 35

Math.floor

Question 36

How do you generate a random number?

Answer 36

math.random float number between 0 and 1 representing a percentage

Question 37

How do you delete an element from an array?

Answer 37

array.splice(index, how many)

Question 38

How do you append an element to an array?

Answer 38

array.push

Question 39

How do you break a string up into an array?

Answer 39

array.split(what it splits by) delimiter

Question 40

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

Answer 40

no. console.log

Question 41

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

Answer 41

no they have return values but you wont always use it

Question 42

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

Answer 42

mdn

Question 43

What is the purpose of a loop?

Answer 43

a way to run a code block until a specific condition is met

Question 44

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

Answer 44

To top the loop from continue running

Question 45

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

Answer 45

how many times it will be running

Question 46

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

Answer 46

after the initialization

Question 47

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

Answer 47

After each iteration

Question 48

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

Answer 48

before running the while loop

Question 49

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

Answer 49

the beginning of the loop

Question 50

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

Answer 50

Break

Question 51

What does the ++ increment operator do?

Answer 51

increases value by 1 by default.

Question 52

How do you iterate through the keys of an object?

Answer 52

for (keys in object) { }

Question 53

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

Answer 53

focus

Question 54

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

Answer 54

blur

Question 55

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

Answer 55

input

Question 56

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

?

Answer 56

'submit' which is fired on the form and not the button. Never have the click event listener on a button

Question 57

What does the event.preventDefault() method do?

Answer 57

preventing the default behavior. for check box it will not show a check. not common you want to rid the default

Question 58

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

Answer 58

if you dont call it, page reloads and refreshes. the data is on the url but irrelevant to the point. based on initial behavior of form behaviors and action attributes. default behavior would submit to same page.

Question 59

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

Answer 59

form.elements has certain properties. numbered properties, named properties in multiple forms. same thing is saved multiple times. email too message too. two out of three are saafety cases. dom is trying to pass it. have property based off of id attribute. user-email will show minus not the whole thing. using .email takes the name attribute. is relevant to form submissions. use a name attribute in every input using dot notation.

Question 60

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

Answer 60

any form control containing the value property is get and set by VALUE

Question 61

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

Answer 61

if it doesn't work, you wont know whats working and not working

Question 62

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

Answer 62

see if there are any errors.

Question 63

Does the document.createElement() method insert a new element into the page?

Answer 63

no

Question 64

How do you add an element as a child to another element?

Answer 64

parent.appendchild(child)

Question 65

What do you pass as the arguments to the element.setAttribute() method?

Answer 65

assigned value to attribute

Question 66

What steps do you need to take in order to insert a new element into the page?

Answer 66

create element then add textcontent if required then parent.appendchild(child) make element, configure with class application or event listener, query for parent element, and then pass argument with appendchild.

Question 67

What is the textContent property of an element object for?

Answer 67

assign value to textcontent

Question 68

Name two ways to set the class attribute of a DOM element.

Answer 68

classname or set attribute or even set list.

Question 69

What are two advantages of defining a function to do create something (like the work of creating a DOM tree)?

Question 70

What is the event.target?

Answer 70

it references the object to which an event happened

Question 71

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

Answer 71

bubbling allows its parents know which of its descendants are being listened to.

Question 72

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

Answer 72

event.target.tagName

Question 73

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

Answer 73

the closest item matching the argument string for css selector returning the nearest parent element with the css selector ancestor or null

Question 74

How can you remove an element from the DOM?

Answer 74

element.remove()

Question 75

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?

Answer 75

event delegation by putting the event listener on the ancestor

Question 76

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

Answer 76

makes the element not visible and not take any space.

Question 77

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

Question 78

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

Question 79

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

Answer 79

every step

Question 80

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 81

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 82

What is JSON?

Answer 82

JSON is a text-based data format

Question 83

What are serialization and deserialization?

Answer 83

Serialization is when code is being transcoded to bits and stored data whereas deserialization is taking the bits and stored data into real code

Question 84

Why are serialization and deserialization useful?

Answer 84

To transmit information through the internet.

Question 85

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

Answer 85

JSON.stringify(file you want serialized)

Question 86

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

Answer 86

JSON.parse(string you want deserialized)

Question 87

What are arrays used for?

Answer 87

To store a list of values

Question 88

Describe array literal notation.

Answer 88

set a variable = to square brackets [] and input items

Question 89

How are arrays different from "plain" objects?

Answer 89

Arrays use index values instead of keys like objects

Question 90

What number represents the first index of an array?

Answer 90

0

Question 91

What is the length property of an array?

Answer 91

it tells the length of the array.

Question 92

How do you calculate the last index of an array?

Answer 92

array at index [array.length]

Question 93

What is a function in JavaScript?

Answer 93

a set of statements that performs a task

Question 94

Describe the parts of a function definition.

Answer 94

it has the keyword function, an optional name, parameters in parenthesis curly brackets executing a statement and an optional return statement with a closing curly bracket for the function code block.

Question 95

Describe the parts of a function call.

Answer 95

using the defined name and simply passing an argument inside parenthesis.

Question 96

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

Answer 96

'function calls' call the defined function. it utilizes it.

Question 97

What is the difference between a parameter and an argument?

Answer 97

parameters are defined within the definition while arguments utilize the function with its values as the parameters used in functions

Question 98

Why are function parameters useful?

Answer 98

They are utilized as variables within the function when the function is called.

Question 99

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

Answer 99

it returns the statement out of the function and ends the function.

Question 100

What is a "model"?

Answer 100

How html page can access and contents update

Question 101

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

Answer 101

the DOM document node

Question 102

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

Answer 102

the different parts of the page loaded in the browser window

Question 103

What is a DOM Tree?

Answer 103

The list of elements attribute and text in the html from parent to child

Question 104

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

Answer 104

getElementby or queryselector

Question 105

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

Answer 105

queryselectorAll

Question 106

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

Answer 106

to access and add methods to the queried return

Question 107

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

Answer 107

console.dir

Question 108

Why would a