DOM

Question 1

What is a “model”?

Answer 1

a representation of something

Question 2

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

Answer 2

html

Question 3

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

Answer 3

object data type

Question 4

What is a DOM Tree?

Answer 4

javascript object for an html element and its children containing attributes and values

Question 5

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

Answer 5

querySelector( )

getElementById( )

Question 6

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

Answer 6

querySelectorAll( )

Question 7

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

Answer 7

to use in the future and easier to find

Question 8

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

Answer 8

console.dir( )

Question 9

Why would a tag need to be placed at the bottom of the HTML content instead of at the top?

Answer 9

HTML content has to load first

Question 10

What does document.querySelector( ) take as its argument and what does it return?

Answer 10

string that contains CSS selector and returns DOM at first occurrence

Question 11

What does document.querySelectorAll( ) take as its argument and what does it return?

Answer 11

string that contains CSS selector and returns Node list

Question 12

What is the purpose of events and event handling?

Answer 12

interactivity

Question 13

Are all possible parameters required to use a JavaScript method or function?

Answer 13

no, some parameters are optional

Question 14

What method of element objects lets you set up a function to be called when a specific type of event occurs?

Answer 14

.addEventListener( )

Question 15

What is a callback function?

Answer 15

function passed as an argument in another function

Question 16

What object is passed into an event listener callback when the event fires?

Answer 16

object with all the data about

Question 17

What is the event.target? If you weren’t sure, how would you check? Where could you get more information about it?

Answer 17

element WHERE the event occurred, check on MDN

Question 18

What is the difference between these two snippets of code?

element. addEventListener(‘click’, handleClick)
element. addEventListener(‘click’, handleClick())

Answer 18

function definition
return value of the function call

Question 19

What is the className property of element objects?

Answer 19

he value of an element’s class attribute

Question 20

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

Answer 20

object.className = ‘class’

Question 21

What is the textContent property of element objects?

Answer 21

represents the text content of the node and its descendants

Question 22

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

Answer 22

object.textContent = ‘text content’

Question 23

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

Answer 23

no

Question 24

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

Answer 24

more complicated

Question 25

Why is storing information about a program in variables better than only storing it in the DOM?

Answer 25

its easier to access and pass as arguments

Question 26

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

Answer 26

focus

Question 27

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

Answer 27

blur

Question 28

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

Answer 28

input

Question 29

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

Answer 29

submit

Question 30

What does the event.preventDefault() method do?

Answer 30

prevents the default behavior for the event

Question 31

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

Answer 31

page refreshes

Question 32

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

Answer 32

elements property

Question 33

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

Answer 33

value property

Question 34

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

Answer 34

harder to spot bug

Question 35

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

Answer 35

you know when somethings not working

Question 36

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

Answer 36

no, it just creates it

Question 37

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

Answer 37

.appendChild()

Question 38

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

Answer 38

(‘name of attribute’, ‘value of attribute’)

Question 39

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

Answer 39

.createElement(), store new element, query for parent element, append onto parent

Question 40

What is the textContent property of an element object for?

Answer 40

retrieve the text or change the text

Question 41

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

Answer 41

setAttribute() or .className

Question 42

What is the event.target?

Answer 42

element where the event occurred

Question 43

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

Answer 43

bubbling

Question 44

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

Answer 44

.tagName

Question 45

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

Answer 45

takes string of selector as argument and returns closest ancestor of the selected element

Question 46

How can you remove an element from the DOM?

Answer 46

Element.remove()

Question 47

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 47

addEventListener to parent event and check if type of event.target is what you want it on

Question 48

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

Answer 48

does not display and taken out of document flow

Question 49

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

Answer 49

it takes a selector in a string and returns a boolean

Question 50

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

Answer 50

.getAttribute()

Question 51

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

Answer 51

every step where a value is changing

Question 52

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?

Answer 52

make new event handler each time you add

Question 53

What is a “callback” function?

Answer 53

function passed into another function as an argument

Question 54

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a JavaScript function until some point in the future?

Answer 54

setTimeout( )

Question 55

How can you set up a function to be called repeatedly without using a loop?

Answer 55

setInterval( )

Question 56

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

Answer 56

0

Question 57

What do setTimeout() and setInterval() return?

Answer 57

an positive integer ID used to pass to clearInterval ( )