DOM

Question 1

What is a “model”?

Answer 1

A template to follow

Question 2

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

Answer 2

the current html document

Question 3

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

Answer 3

The elements of the document are represented as objects

Question 4

What is a DOM tree?

Answer 4

A visual representation of all of the document’s nodes and their relation to one another

Question 5

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

Answer 5

document. querySelector(‘css selector’)

document. getElementById(‘id’)

Question 6

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

Answer 6

document. querySelectorAll( )
document. getElementsByClassName( )
document. getElementsByTagName( )

Question 7

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

Answer 7

The variable does not hold the value of the node itself, but a reference to where that node is stored. So, if you want to do multiple things to that node, it is useful to store it in a variable so that the computer does not have to search for it every time

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

The browser needs to parse through the entire HTML body

Question 10

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

Answer 10

It takes in a CSS selector and returns the first element that matches the result

Question 11

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

Answer 11

CSS selector as argument

Returns a NodeList of all elements that match

Question 12

What is the purpose of events and event handling?

Answer 12

Makes the page more interactive by triggering scripts when certain events happen

Question 13

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

Answer 13

.addEventListener(event, callback function)

Question 14

What is a callback function?

Answer 14

A function that is passed as an argument into another function.

A function that you don’t want to call right away so you store for later

Question 15

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

Answer 15

the event object

Question 16

What is the event.target? If you’re not sure, where would you find information about it?

Answer 16

property that returns the object which the event was bounded onto

Question 17

Difference between:

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

Answer 17

The first one is a callback function; Only runs when the event occurs

Second one is a normal function call and it runs as the web page is loaded only.

Question 18

What is the className property of element objects?

Answer 18

returns a string of the value of the class attribute for the element

Question 19

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

Answer 19

update the className property of the element

Question 20

What is the textContent property of element objects?

Answer 20

Gets the text content of the element as well as the text content of its children(?)

Question 21

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

Answer 21

with the .textContent property of an element

Question 22

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

Answer 22

No, but always present. Do not forget event parameter when defining event handler functions

Question 23

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

Answer 23

More difficult as the click counter allows us to control both the text content and the button color

Question 24

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

Answer 24

It is easier to reference especially if using multiple times

Question 25

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

Answer 25

focus event

Question 26

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

Answer 26

blur event

Question 27

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

Answer 27

‘input’ event

Question 28

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

Answer 28

‘submit’ event

Question 29

What does the event.preventDefault( ) do?

Answer 29

tells browser that even if an event does not get explicitly handled, its default action should not be taken

Question 30

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

Answer 30

The page will refresh with the user’s inputs added to the URL

Question 31

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

Answer 31

form.elements

array-like object(?) that you can access via indexes

Question 32

What property of a form control object lets you get and set its value?

Answer 32

.value

Question 33

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

Answer 33

Will inevitably run into bugs/errors and it will be much harder to debug if there’s a lot of code to go through

Question 34

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

Answer 34

Can see if any errors are occurring and confirm the program is running as expected.

Question 35

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

Answer 35

No; need the appendChild( ) method

Question 36

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

Answer 36

parent-element.appendChild(aChild)

.append( )

Question 37

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

Answer 37

setAttribute(attribute, value)

Question 38

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

Answer 38

Create a new element and assign it to a variable
Use the variable to assign textContent to it
append the new element onto a parent with appendChild

Question 39

What is the textContent property of an element object for?

Answer 39

Gets or sets the text node of an element

Question 40

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

Answer 40

element. className
element. setAttribute( )
element. classList.remove( )

Question 41

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

Answer 41

Helps break down the work you need into chunks as well as allow you to re-use/repeat the function as many times as needed

Question 42

Give two examples of media features that you can query in an @media rule?

Answer 42

width

orientation

Question 43

Which HTML meta tag is used in mobile-responsive web design?

Answer 43

meta name=”viewport” content=”width=device-width, initial-scale=1.0”

Question 44

What is the event.target?

Answer 44

the element that the user actually interacted with, but as a result of event bubbling, it caused an event to get triggered

Question 45

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

Answer 45

Event bubbling

Question 46

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

Answer 46

element.tagName

Question 47

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

Answer 47

takes in a css selector as argument and returns the closest ancestor that matches

Question 48

How can you remove an element from the DOM?

Answer 48

element.remove( )

Question 49

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 49

By adding the event listener to a parent and then relying on event bubbling and conditions to find the actual element you want