DOM

Question 1

What is a “model”?

Answer 1

A representation or recreation of an original

Question 2

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

Answer 2

The HTML document

Question 3

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

Answer 3

Refers to a JavaScript object

Question 4

What is a DOM Tree?

Answer 4

The DOM tree is a model of a web page

Question 5

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

Answer 5

• getElementById()

- querySelector() – only use querySelector

Question 6

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

Answer 6

• getElementsByClassName()
• getElementsByTagName()
• querySelectorAll()

Question 7

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

Answer 7

To save the browser from needing to look up the same elements again if it is intended to be reused.

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 script tag need to be placed at the bottom of the HTML content instead of at the top?

Answer 9

So the html content can load first

Question 10

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

Answer 10

• String argument is a CSS Selector (type, class id)

- Returns the first matching element

Question 11

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

Answer 11

• String argument is a CSS Selector (type, class id)

- Returns all matching elements in a node list

Question 12

How do you query for attributes?

Answer 12

(element + attrtype + attrname)

document.querySelector(‘p#explanation’)

Question 13

What is the DOM?

Answer 13

Representation of a JavaScript object describing the html document

Question 14

What is the purpose of events and event handling?

Answer 14

Enable functionality with events on the webpage

Question 15

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

Answer 15

No

Question 16

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

Answer 16

addEventListener() method

Question 17

What is a callback function?

Answer 17

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action

Question 18

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

Answer 18

Event object

Question 19

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

Answer 19

A reference to the object onto which the event was dispatched

Learn more with:
console.dir(event.target)

Question 20

What is the className property of element objects?

Answer 20

It gets and sets class to an element

Question 21

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

Answer 21

$element.className = “classone classtwo“

Question 22

What is the textContent property of element objects?

Answer 22

textContent property allows you to get and set the text inside a node

Question 23

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

Answer 23

node.textContent = “Assign text value”

Question 24

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

Answer 24

No

Question 25

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

Answer 25

• More complicated
• Stick to one source of truth, always keep data in
  JS instead of the DOM

Question 26

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

Answer 26

Simplify the source of data, and prevent bugs

Question 27

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

Answer 27

No

Question 28

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

Answer 28

• attribute type
• value

$element.setAttribute(‘id’, ‘home’)

Question 29

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

Answer 29

element.appendChild($childElement)

Question 30

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

Answer 30

document. createElement(el)
- save into variable

query DOM for parent element that exists on HTML page
- save into variable

parentEl.appendChild(childEl)

Question 31

What is the textContent property of an element object for?

Answer 31

textContent will get and set text to an existing node

Question 32

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

Answer 32

• className
• setAttribute(‘class’ ‘value’)
• classList.add()

Question 33

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

Answer 33

• reusability

- faster to create it once and have a loop handle it

Question 34

What is the event.target?

Answer 34

event.target is the the location of where the event occurred

Question 35

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

Answer 35

An event is carried up through the event-chain due to bubbling

Question 36

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

Answer 36

event.target.tagName

Question 37

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

Answer 37

The closest method traverses the element and it’s parent and returns closest ancestor of the selected element

Question 38

How can you remove an element from the DOM?

Answer 38

$element.remove()

Question 39

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 39

Add the event listener to the closest parent element that contains all the clickable DOM elements