DOM

Question 1

Why do we log things to the console?

Answer 1

to see what our code is doing

Question 2

What is a “model”?

Answer 2

a representation of something else

Question 3

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

Answer 3

the HTML document

Question 4

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

Answer 4

referring to the JavaScript objects that the DOM reads the document as

Question 5

What is a DOM Tree?

Answer 5

all the nodes of an element; a model of a web page the browser stores in memory (DOM element plus all the children inside 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

getElementByClassName( )
getElementByTagName( )
querySelectorAll( )

Question 8

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

Answer 8

if you want to work with that element node more than once

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 the elements of the HTML page before the JavaScript code can access them

Question 11

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

Answer 11

argument: a string containing a CSS selector describing the element you want to work with
return: ONE HTMLElement object representing the first element in the document that matches the selector

Question 12

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

Answer 12

argument: DOMString containing one or more selectors
return: a NodeList containing one Element object for each element that matches at least one of the specified selectors, otherwise an empty NodeList if none match

Question 13

Why do we log things to the console?

Answer 13

to see how our code is working

Question 14

What is the purpose of events and event handling?

Answer 14

allows your page to be interactive

Question 15

What do [ ] square brackets mean in function and method syntax documentation?

Answer 15

it means it is optional to include

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 function that gets passed into another function as an argument which is called within the outer function to do some action

• a function being passed as data

Question 18

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

Answer 18

the 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

An HTML element that triggered this event

you can console log it and check mdn for more information

Question 20

What is the difference between these two snippets of code?

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

Answer 20

the first one runs the handleClick function when the event is fired

the second one indicates that the handleClick function should run as the page loads

Question 21

What is the className property of element objects?

Answer 21

string value containing each class for the element separated by spaces

Question 22

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

Answer 22

elm.setAttribute(‘class’, elm.getAttribute(‘class’))

Question 23

What is the textContent property of element objects?

Answer 23

represents the text content of the node and its descendants.

Question 24

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

Answer 24

use textContent property on the element object and assign it a new value

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 difficult

Question 27

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

Answer 27

allows to reuse more than once simply and efficiently, easier to read

Question 28

What does the transform property do?

Answer 28

lets you rotate, scale, skew or translate an element

Question 29

Give four examples of CSS transform functions.

Answer 29

matrix, translate, rotate, skew, scale

Question 30

What is the event.target?

Answer 30

target property of event interface, reference to element where the event originated from

Question 31

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

Answer 31

bubbling (elaborate)

Question 32

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

Answer 32

tagName?

Question 33

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

Answer 33

argument: selector
return: closest ancestor

Question 34

How can you remove an element from the DOM?

Answer 34

remove( )

Question 35

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 35

dom event delegation

putting an event listener on the element above the element you want it to originate on