LFZ DOM Quiz

Question 1

Why do we log things to the console?

Answer 1

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 HTML Document

Question 4

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

Answer 4

getElementById, and querySelector

Question 5

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

Answer 5

getElementsByClassName

Question 6

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

Answer 6

To cache the location of the element so that the browser doesn’t have to find the element all over again

Question 7

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

Answer 7

To cache the reference of the element so that the browser doesn’t have to find the element all over again

Question 8

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

Answer 8

So that the browser can analyze all of the data in the HTML

Question 9

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

Answer 9

console.dir

Question 10

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

Answer 10

it takes in a css selector and returns a nodelist of all elements with the css class

Question 11

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

Answer 11

it takes in a css selector and returns the first element it finds that matches

Question 12

Why do we log things to the console?

Answer 12

For debugging things

Question 13

What is the purpose of events and event handling?

Answer 13

To listen for things like mouse click, key down, etc

Question 14

What is the purpose of events and event handling?

Answer 14

To listen for things like mouse click, key down, etc and then do things

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 call back function is a function that takes in a function as an argument

Question 17

What is a callback function?

Answer 17

A call back function is a function that takes in a function as an argument and runs it

Question 18

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

Answer 18

an 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 target element of the event, you can check the documentation, or you can log the value to the console

Question 20

What is the difference between these two snippets of code?

Answer 20

The first one is passing the function through

The second one is calling the function and running the code

Question 21

What is the className property of element objects?

Answer 21

The class of the element

Question 22

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

Answer 22

by changing the className property

Question 23

What is the textContent property of element objects?

Answer 23

the text content of the element. It excludes markup

Question 24

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

Answer 24

by changing the textContent property of the selected element

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

Simpler

Question 28

What is the event.target?

Answer 28

The target node of the event

Question 29

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

Answer 29

due to event bubbling. Clicking on a child element, also targets parent elements

Question 30

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

Answer 30

event.tagName

Question 31

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

Answer 31

It takes in a css selector and returns the closest parent that has that tag. Can return itself

Question 32

How can you remove an element from the DOM?

Answer 32

with the remove method

Question 33

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 33

By putting the event listener on a parent container, and appending the new element as a child to that parent