DOM (Document Object Model)

Question 1

Why do we log things to the console?

Answer 1

Inspect value to debug - This is especially important for DOM

Question 2

What is a “model”? (Not in relation to code)

Answer 2

A prototype or representation of something

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

Objects in JavaScript

Question 5

What is a DOM Tree?

Answer 5

JavaScript object for a HTML element including attributes, values, and its children elements

Question 6

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

Answer 6

getElementByID

querySelector (preferred method)

Question 7

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

Answer 7

querySelectorAll (preferred method)

Question 8

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

Answer 8

Easier access so you can search for it and use it again in the future

Question 9

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

Answer 9

console.dir (which stands for directory)

Question 10

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

Answer 10

HTML content needs to load the data before using DOM or else it will have nothing to work with

Question 11

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

Answer 11

String that consists of a CSS selector and returns the first matching element

Question 12

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

Answer 12

String that consists of a CSS selector and returns all those that match (node list)

Question 13

What is the purpose of events and event handling?

Answer 13

Creating a reaction in response to something happening.

Question 14

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

Answer 14

No some are optional

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 within a function that is being passed as another argument

Question 17

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

Answer 17

Object that contains the data of that event

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

Where the event occurred.

You can check in the console.log

Question 19

What is the difference between these two snippets of code?

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

Answer 19

The first will run when the event fires.
The second will return the value which would be undefined. We will never call the event listener, the browser technically does this which is why the second code snippet is wrong.

Question 20

What is the className property of element objects?

Answer 20

Property stored on the DOM element object which stores the class attribute of that element

Question 21

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

Answer 21

className property with a value assignment

Question 22

What is the textContent property of element objects?

Answer 22

Allows us to retrieve or manipulate text content

Question 23

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

Answer 23

textContent property with a value assignment

Question 24

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

Answer 24

Not always - all the information isn’t always necessary

Question 25

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

Answer 25

You can reuse it later and you don’t want to intermingle your languages in a way where they become dependent on each other.

Question 26

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

Answer 26

No

Question 27

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

Answer 27

appendChild method

Question 28

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

Answer 28

String name and then the value

Question 29

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

Answer 29

• createElement
• Store the new element
• Query for parent element
• Call appendChild on parent with new element as an argument

Question 30

What is the textContent property of an element object for?

Answer 30

Stores textContent of the HTML element to retrieve or change

Question 31

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

Answer 31

className

setAttribute

Question 32

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

Answer 32

Reusable and its easier to debug and test for it’s intended purpose.

Question 33

What is the event.target?

Answer 33

Element where the event occurs

Question 34

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

Answer 34

Bubbling

Question 35

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

Answer 35

tagName

Question 36

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

Answer 36

String of CSS selector and returns closest ancestor element that matches pattern

Question 37

How can you remove an element from the DOM?

Answer 37

remove method

Question 38

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 38

Add an eventListener to parent element and then run a condition to see if it is targeting an element