DOM

Question 1

Why do we log things to the console?

Answer 1

To verify that the result is what we’re expecting

Question 2

What is a “model”?

Answer 2

A representation/recreation of the actual thing. In this case, a DOM tree

Question 3

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

Answer 3

The HTML/web page

Question 4

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

Answer 4

JavaScript object

Question 5

What is a DOM Tree?

Answer 5

Data representation of all the objects in the document. Any of the element and all of its child and content

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(), getElementsByClassName(), getElementsByTagName()

Question 8

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

Answer 8

If you want to reuse the query

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

The browser needs to parse all of 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 will take 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

It will take a CSS selector and returns all matching elements in a node list

Question 13

Why do we log things to the console?

Answer 13

To verify that the result is what we’re expecting

Question 14

What is the purpose of events and event handling?

Answer 14

So our script can respond to certain events/user inputs

Question 15

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

Answer 15

No, having a parameter for a function doesn’t mean that it will be used

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

What is a callback function? Function passed into another function as an argument to be used later

Question 17

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

Answer 17

Event object - function as the call back function

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

The target property returns the element that triggered the event. Check on MDN. The element where our target originated from (not attached)

Question 19

What is the difference between these two snippets of code?

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

Answer 19

first one is a variable, second is a function being called. Event handler is the function run when an event listener is run.

Question 20

What is the className property of element objects?

Answer 20

It’s used to update or retrieve the class name on an element

Question 21

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

Answer 21

Get the element and assign the new class name property

Question 22

What is the textContent property of element objects?

Answer 22

To add or update text within a specific element

Question 23

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

Answer 23

Using textcontent property on the DOM property and assigning it the new text content

Question 24

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

Answer 24

No, it’s not always necessary. The event object was not used.

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

It would be more complicated

Question 26

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

Answer 26

We don’t want to have to look elsewhere for the information. Keep the JavaScript data in JavaScript.

Question 27

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

Answer 27

No

Question 28

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

Answer 28

anotherElement.appendChild(element)

Question 29

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

Answer 29

(‘attribute name’, ‘value’)

Question 30

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

Answer 30

Create new element stored in a variable (createElement), create new text stored in a variable (createTextNode), attach text node to element with appendChild, find the position where the new element stored in a variable, insert new element into its position with appendChild().

Question 31

What is the textContent property of an element object for?

Answer 31

Setting or returning the text content of specified node and all its descendants

Question 32

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

Answer 32

className or setAttribute

Question 33

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

Answer 33

Use it in a addEventListener, use the function over again

Question 34

What is the event.target?

Answer 34

The target property returns the element that triggered the event

Question 35

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

Answer 35

Because of event bubbling. Event is being carried forward to each ancestor of the chain

Question 36

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

Answer 36

tagName

Question 37

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

Answer 37

It takes a string CSS selector and returns closest ancestor of it

Question 38

How can you remove an element from the DOM?

Answer 38

elementToRemove.remove()

Question 39

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 39

By delegating the event to the parent element that contains all the clickable elements