Document Object Model

Question 1

Why do we log things to the console?

Answer 1

We log things to the console for debugging purposes.

Question 2

What is a “model”?

Answer 2

The DOM Tree. Model is a representation/copy of the original.

Question 3

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

Answer 3

The HTML document is being referred to in the phrase Document Object Model.

Question 4

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

Answer 4

JavaScript object.

Each object represents a different part of the page loaded in the browser window.

Question 5

What is a DOM Tree?

Answer 5

A tree/structure that shows all nodes/chunks of the HTML document.

Question 6

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

Answer 6

document. querySelector( )

document. getElementById( )

Question 7

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

Answer 7

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

Question 8

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

Answer 8

We might want to assign a return value of a DOM query to a variable so that it is reusable.

Question 9

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

Answer 9

console.dir( )

Short for “directory”.

Question 10

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

Answer 10

The «a>script</a>> tag needs to be placed at the bottom of the HTML content because the HTML content should load first on the browser.

Question 11

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

Answer 11

It takes a CSS selector as its argument and returns the first element with that CSS selector.

Question 12

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

Answer 12

It takes a CSS selector as its argument and returns all elements with that CSS selector.

Question 13

Why do we log things to the console?

Answer 13

For debugging purposes.

And to check if something is working.

Question 14

What is the purpose of events and event handling?

Answer 14

The purpose is to add interactive properties to the website for the users.

Add dynamic content.

Ability to have something occur and do something in response.

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

A callback function is a function being passed around as a value.

Question 18

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

Answer 18

The event object.

The event object includes the target property.

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 event target is the place/element where the event actually began/occurred. If not sure, we can console.log it and get more information in the console.

Question 20

What is the difference between these two snippets of code?

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

Answer 20

A function is being passed in as an argument in the first snippet.

A function is being called as an argument in the second snippet. (This would not work)

Question 21

What is the className property of element objects?

Answer 21

The className property is the property that holds the class names attached to that element object.

Question 22

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

Answer 22

You can update the CSS class attribute of an element by:

$element.className = new class name

Question 23

What is the textContent property of element objects?

Answer 23

The textContent property is the property that holds the text content attached to that element object/node.

Question 24

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

Answer 24

You can update the text within an element by:

$element.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

It would be more complicated.

Question 27

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

Answer 27

It doesn’t have to go to the HTML document to find the data that is desired every time.

Keep JavaScript things in JavaScript.

Question 28

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

Answer 28

No.

Question 29

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

Answer 29

appendChild( )

Question 30

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

Answer 30

The name of attribute and value of the attribute.

Question 31

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

Answer 31

querySelector
createElement
appendChild

Question 32

What is the textContent property of an element object for?

Answer 32

It is to set or get the text of that element.

Question 33

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

Answer 33

setAttribute( )

className property

Question 34

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

Answer 34

Reusability.

Variability.

Question 35

What is the event.target?

Answer 35

The object for the dom element where the event was fired.

event.target stores the element where the event originated from.

Question 36

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

Answer 36

Event bubbling. (Most specific to least specific)

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 CSS selector and it returns the closest ancestor element with the matching selector. (Goes up the tree and look for the element with the matching selector)

Question 39

How can you remove an element from the DOM?

Answer 39

elementName.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

Add an event listener onto the parent element.