DOM

Question 1

Why do we log things to the console?

Answer 1

To check that our code is doing what we intended for it to do

Question 2

What is a “model”?

Answer 2

Representation of how the html page is structured

Question 3

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

Answer 3

HTML document

Question 4

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

Answer 4

Datatype object (in JavaScript)

Question 5

What is a DOM Tree?

Answer 5

Collection of html elements (like a family tree) AND all of its child elements as well as any relevant information attached to them

Question 6

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

Answer 6

o	getElementbyID(‘id’)
o	querySelector(‘css selector’)

Question 7

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

Answer 7

o	getElementsByClassName(‘class’)
o	getElementsByTagName(‘TagName’)
o	querySelectorAll(‘css selector’)

Question 8

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

Answer 8

To allow browser to locate the element faster in the DOM (if you’re going to be using this return value more than once)

Question 9

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

Answer 9

console.dir( )

Question 10

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

Answer 10

Because the browser needs to read all the elements in the HTML page before JavaScript can access them

Question 11

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

Answer 11

It takes a STRING containing a CSS selector and returns the first DOM element object with that selector.

Question 12

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

Answer 12

It takes a STRING containing a CSS selector and gives a NodeList of elements.

Question 13

What is the purpose of events and event handling?

Answer 13

To make webpages interactive

Question 14

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

Answer 14

No

Question 15

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

Answer 15

.addEventListener( )

Question 16

What is a callback function?

Answer 16

Function that you pass inside another function as an argument

Question 17

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

Answer 17

Event object (object passed by JS that has all the information about the event that occured)

Question 18

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

Answer 18

A read-only property that shows which object(or html element) triggered the event

Check through the console log and see which element gets logged

Question 19

What is the difference between these two snippets of code?

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

Answer 19

1 has a callback function

2 has the return of the function call

Question 20

What is the className property of element objects?

Answer 20

Sets and returns the class name of a specified element

Question 21

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

Answer 21

By using element.className = ‘new-class-name-in-html-format’

Question 22

What is the textContent property of element objects?

Answer 22

Represents the text content of the node

Question 23

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

Answer 23

By using node.textContent = ‘newtext’

Question 24

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

Answer 24

No sometimes you have the information you need without the parameters

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

Complicated- because it wouldn’t be easy to tell what our current number is at

Question 26

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

Answer 26

Easy to make future updates when information is easily visible and accessible

Question 27

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

Answer 27

Focus

Question 28

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

Answer 28

Blur

Question 29

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

Answer 29

Input

Question 30

What event is fired when a user clicks the "submit" button within a < form > ?

Answer 30

Submit

Question 31

What does the event.preventDefault() method do?

Answer 31

Prevents default action normally taken by the implementation of a method from happening

Question 32

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

Answer 32

When the submit button is clicked, the page will reload immediately

Question 33

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

Answer 33

.elements

Question 34

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

Answer 34

value

Question 35

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

Answer 35

No, because it needs to be added to the DOM for it to be visible

Question 36

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

Answer 36

.appendChild( insert new child element)

Question 37

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

Answer 37

setAttribute('name', value)

Question 38

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

Answer 38

``` o Create the element: document.createElement() o Save(assign) element to the variable o Append the element into a parent node: .appendChild() ```

Question 39

What is the textContent property of an element object for?

Answer 39

For inserting text into a node and its children

Question 40

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

Answer 40

``` o element.ClassName = ‘whatever-class-name’ o setAttribute('name', value) ```

Question 41

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

Answer 41

o You can create a bulk of html code to insert all at once | o Function can be reused

Question 42

What is the event.target?

Answer 42

Read-only property that tells you which element the event occurred (dispatched from) on

Question 43

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

Answer 43

Due to event bubbling as it continues to look up the ancestral tree

Question 44

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

Answer 44

event.target.tagName

Question 45

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

Answer 45

o Takes a string with a css selector | o Returns the closest element that matches that selector

Question 46

How can you remove an element from the DOM?

Answer 46

.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

By using an if statement to check if the event.target property is equal to the actual clicked element (mostly element but it doesn’t have to be strictly only an element – could be something else)

Question 48

What is the event.target?

Answer 48

Read-only property that tells you which element the event occurred (dispatched from) on

Question 49

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

Answer 49

It removes the element from the document flow

Question 50

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

Answer 50

o String of a css selector (in a css form) | o Gives back a Boolean value

Question 51

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

Answer 51

.getAttribute(‘string of the attribute you want to get the value of’)

Question 52

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

Answer 52

After every step

Question 53

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 53

You’d have to write an individual function for each tab

Question 54

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?

Answer 54

You’d have to write multiple if-else statements for each views