DOM

Question 1

What is a “model”?

Answer 1

a tree

Question 2

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

Answer 2

html file

Question 3

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

Answer 3

data type objects

Question 4

What is a DOM Tree?

Answer 4

model structure

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

for reusability and so you can access other information within the DOM object

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

so that when the user first load the page, all content can get loaded up first before DOM

Question 10

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

Answer 10

string of css selector, return first matched item

Question 11

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

Answer 11

string of css selector, return nodeList of all the matched items

Question 12

What is the purpose of events and event handling?

Answer 12

prepare of incoming actions and response with something (interactive)

Question 13

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

Answer 13

no

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 that is passed into another function (not calling it)

Question 16

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

Answer 16

event data

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

event target is the element that the event originated from, console log it, MDN

Question 18

What is the difference between these two snippets of code?
1- element.addEventListener(‘click’, handleClick)
2- element.addEventListener(‘click’, handleClick())

Answer 18

1 - is set with a callback function
2 - the function will run on opening the webpage

Question 19

what is event bubbling?

Answer 19

event that happen to the element, it happens to the ancestor elements as well
Div > button -> click on button = click on Div

Question 20

What is the className property of element objects?

Answer 20

value of the attribute class of HTML document

Question 21

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

Answer 21

element.className = ‘new_value new_value_2’

Question 22

What is the textContent property of element objects?

Answer 22

property that hold the text for that element

Question 23

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

Answer 23

element.textContent = ‘new value’

Question 24

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

Answer 24

no

Question 25

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

Answer 25

doesn’t make javascript depends on other language when accessing data

Question 26

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

Answer 26

no

Question 27

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

Answer 27

parent.appendChild(child_node)

Question 28

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

Answer 28

(‘attribute_name’, ‘value’)

Question 29

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

Answer 29

• create new element -> store it to variable
• add necessary attribute/value/text
• append this element to any other parents (if needed)
• querySelector() parent element that is existed on the page
• then append to parent element

Question 30

What is the textContent property of an element object for?

Answer 30

to insert text content to any element

Question 31

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

Answer 31

element.setAttribute(), document.className

Question 32

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

Answer 32

so it can be dynamic and create any amount of data depend on input data

Question 33

What is the event.target?

Answer 33

where the event occur

Question 34

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

Answer 34

event bubbling

Question 35

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

Answer 35

.tagName or nodeName (return as string all CAP)

Question 36

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

Answer 36

CSS selector
return element selected first found

Question 37

How can you remove an element from the DOM?

Answer 37

element.remove()

Question 38

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 38

adding even listener to the parent and target specific tag name when event trigger

Question 39

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

Answer 39

not displaying item and completely remove it from the document flow

Question 40

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

Answer 40

CSS selector, return boolean (true or false)

Question 41

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

Answer 41

.getAttribute(‘attribute_name’)