DOM

Question 1

Why do we log things to the console?

Answer 1

For debugging and an easy way to inspect your variables in the browser

Question 2

What is a “model”?

Answer 2

Replica

Question 3

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

Answer 3

The HTML

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

DOM element and all of the items in it

Question 6

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

Answer 6

getElementById()

querySelector()

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

For reusability and accessibility

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 run the html document first in order to create a DOM

Question 11

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

Answer 11

CSS selector and it returns the first element from the document

Question 12

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

Answer 12

CSS selector and it returns NodeList of all elements matching the selector

Question 13

What is the purpose of events and event handling?

Answer 13

Events are actions or occurrences that happen in the system

Event handling is steps to trigger some JavaScript code

Question 14

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

Answer 14

No

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

A callback function is a function passed into another function as an argument

Question 17

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

Answer 17

An object with all of the possible data the browser can provide

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 of the Event interface is a reference to the object onto which the event was dispatched

Question 19

What is the difference between these two snippets of code?

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

Answer 19

In the first snippet, the event listener will call on the handleClick function only when the event occurs
In the second snippet, the event listener is calling on the handleClick function but that immediately calls the function

Question 20

What is the className property of element objects?

Answer 20

Gets and sets the value of the class attribute of the specified element.

Question 21

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

Answer 21

Assign a string with new property name to the className property of element object

Question 22

What is the textContent property of element objects?

Answer 22

Represents the text content of the node and its descendants.

Question 23

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

Answer 23

Assign a string with new text to the textContent property of element object

Question 24

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

Answer 24

No

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

No, we would need the variable to keep track of number of clicks or we would have to make a new variable every time

Question 26

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

Answer 26

For easy reusability and accessibility

Question 27

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

Answer 27

It does not

Question 28

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

Answer 28

element.appendChild()

Question 29

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

Answer 29

The name and the value of the attribute

Question 30

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

Answer 30

Create the element, give it content, add it to the dom

Question 31

What is the textContent property of an element object for?

Answer 31

Represents the text content of the node and its descendants.

Question 32

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

Answer 32

element. setAttribute()

element. className

Question 33

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

Answer 33

Saves time in the long rung

Easy to reuse

Question 34

What is the event.target?

Answer 34

The target of the event (most specific element interacted with)

Question 35

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

Answer 35

Because of event bubbling
When an event happens on an element, it first runs the handlers on it, then on its parent, then all the way up on other ancestors.

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

Takes a DOMString containing a selector list

Returns the element which is the closest ancestor of the selected element

Question 38

How can you remove an element from the DOM?

Answer 38

Element.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

Add the DOM element inside the parent node containing the other DOM elements