DOM

Question 1

Why do we log things to the console?

Answer 1

To make sure our code works

Question 2

What is a “model”?

Answer 2

A representation of an object that is typically smaller than the object that is being modeled

Question 3

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

Answer 3

The html document being loaded into a browser

Question 4

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

Answer 4

Each individual elements on the html page (including the document itself)

Question 5

What is a DOM Tree?

Answer 5

The drawn mapping of the elements of the html page

Question 6

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

Answer 6

querySelector(‘css selector’)

getElementById(‘id’)

Question 7

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

Answer 7

querySelectorAll(‘css selector’)

getElementsByClassName(‘class’)

Question 8

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

Answer 8

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

Question 9

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

Answer 9

console.dir(variableName)

Question 10

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

Answer 10

The browser needs to parse all of the elements in the HTML page before the JavaScript code can access them.

Question 11

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

Answer 11

It takes any valid CSS selector as its argument

Returns the first matching element

Question 12

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

Answer 12

It takes any valid CSS selector as its argument

Returns all matching elements in a node list

Question 13

Why do we log things to the console?

Answer 13

To make sure our code works

Question 14

What is the purpose of events and event handling?

Answer 14

Events are any changes to a document whether it be from user interaction or changes from within the browser.
Event handlers trigger functions depending on the event

Question 15

What do [] square brackets mean in function and method syntax documentation?

Answer 15

They represent optional arguments

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

element.addEventListener(‘event’, callbackFunction);

Question 17

What is a callback function?

Answer 17

A function that is passed as an argument in another function’s call

Question 18

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

Answer 18

The 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

It’s full html element being targeted by a dom query

You could check by logging onto the console or check mdn documentation

Question 20

What is the difference between these two snippets of code?

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

Answer 20

The first one takes a callback function as the argument and the second one runs the function and whatever that is returned will be used as the argument for the addEventListener method

Question 21

What is the className property of element objects?

Answer 21

It accesses the class attribute of an html element

Question 22

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

Answer 22

Query the dom for an element then use the className property to assign a string value to update the class name

Question 23

What is the textContent property of element objects?

Answer 23

It accesses all text within the opening and closing tags of an element

Question 24

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

Answer 24

Query the dom for an element then use the textContent property to assign a string value to update the text content

Question 25

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

Answer 25

No, sometimes you’ll want to write code that applies to other parts of the html document not pertaining to the element the event it targeting

Question 26

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

Answer 26

More complicated. Probably would have to use a loop

Question 27

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

Answer 27

If you store information in the DOM, other parts of your javascript code could potentially change it

Question 28

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

Answer 28

No it only creates a reference to a dom element

Question 29

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

Answer 29

$parent.appendChild($newElement)

Question 30

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

Answer 30

2 arguments: first argument is the html attribute, second argument is the value

Question 31

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

Answer 31

createElement(), setAttribute()(optional), createTextNode()(optional), appendChild()

Question 32

What is the textContent property of an element object for?

Answer 32

Sets or gets the text within the opening and closing tags of an element

Question 33

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

Answer 33

setAttribute(‘class’, ‘value’)

$element.className = ‘value’

Question 34

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

Answer 34

You can reuse that function in several parts of your code

It’s easier to debug a function rather than a whole js document

Question 35

What is the event.target?

Answer 35

It references the object in which the event was directed at

Question 36

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

Answer 36

Using event flow, you can bubble up to the descendent’s ancestor

Question 37

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

Answer 37

tagName

Question 38

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

Answer 38

It takes a selectors as an argument and

It returns the closest element with that selector name to the element that called closest()

Question 39

How can you remove an element from the DOM?

Answer 39

element.remove()

Question 40

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 40

Event delegation