DOM

Question 1

Why do we log things to the console?

Answer 1

To see what is going on, for debugging purposes

Question 2

What is a “model”?

Answer 2

A representation of something

Question 3

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

Answer 3

the webpage itself

Question 4

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

Answer 4

the HTML page

Question 5

What is a DOM Tree?

Answer 5

The pathways of elements and their children

Question 6

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

Answer 6

querySelector

getElementById

Question 7

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

Answer 7

querySelectorAll

Question 8

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

Answer 8

To prevent repeated queries to the DOM, just reuse the variable

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

Answer 10

To allow the HTML code to be parsed first, then JavaScript can read them
(The elements need to be put on the DOM first, then moved around with JS)

Question 11

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

Answer 11

CSS selector as argument, and returns the location of the element selected

Question 12

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

Answer 12

CSS selector as argument, and returns a Node List

Question 13

Why do we log things to the console?

Answer 13

For debugging, check results of javascript code

Question 14

What is the purpose of events and event handling?

Answer 14

Listening for user interactions with the page

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

Question 17

What is a callback function?

Answer 17

When a function is passed into anothe function or method

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

The element at the point of interaction in the DOM

Question 20

What is the difference between these two snippets of code?

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

Answer 20

1st one sets handleClick as a callback function. 2nd one calls the function within the arguments, thus passing the return value as the second argument.

Question 21

What is the className property of element objects?

Answer 21

A property that receives and assigns the class attribute of the target element

Question 22

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

Answer 22

object.classname = ‘updated class attribute’;

Question 23

What is the textContent property of element objects?

Answer 23

It represents the text content of a node and its descendants

Question 24

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

Answer 24

object.textContent = ‘New text content’;

Question 25

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

Answer 25

No

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

Question 27

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

Answer 27

It is easier to manage variables than having to query the DOM repeatedly.

Question 28

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

Answer 28

focus event

Question 29

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

Answer 29

blur event

Question 30

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

Answer 30

input event

Question 31

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

Answer 31

submit event

Question 32

What does the event.preventDefault() method do?

Answer 32

It prevents the page from reloading after the submit event

Question 33

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

Answer 33

It would reload the page after the submit event

Question 34

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

Answer 34

form element’s elements property

Question 35

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

Answer 35

value attribute

Question 36

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

Answer 36

Not being able to see which part of the code is creating a possible error

Question 37

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

Answer 37

Being able to check for errors, and confirming values are printing as expected while code is being written

Question 38

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

Answer 38

No, it just creates the element. appendChild() must be used to insert into the page.

Question 39

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

Answer 39

parentChild.appendChild(childElement)

appends the child as the last child of the parentChild

Question 40

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

Answer 40

attribute type, attribute value

Question 41

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

Answer 41

createElement()
appendChild() to an existing element in the page
append() can also be used (check MDN)

Question 42

What is the textContent property of an element object for?

Answer 42

To set or change the text content of an element
text content can be created and assigned to a new element
using textContent does destroy other child elements that currently exists in the designated element

Question 43

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

Answer 43

setAttribute(class, )

object.className

Question 44

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

Answer 44

A function can be repeated for different object values, and the return value of the function can be easily managed like a variable

Question 45

What is the event.target?

Answer 45

the element that was interacted with in the webpage

Question 46

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

Answer 46

event bubbling

Question 47

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

Answer 47

.tagName

.nodeName is also applicable, but .tagName is needed to retrieve an actual element

Question 48

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

Answer 48

It takes a CSS Selector as its argument and returns the node that matches that CSS Selector

Question 49

How can you remove an element from the DOM?

Answer 49

querySelector to find the element node

element.remove()

Question 50

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 50

use addEventListener on the parent element