DOM

Question 1

Why do we log things to the console?

Answer 1

to check if the code is working properly and giving the expected output

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 page

Question 4

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

Answer 4

the nodes of the HTML elements, which are JS objects

Question 5

What is a DOM Tree?

Answer 5

a model of the HTML page, composed of nodes

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

so you can use the variable when you need a specific element instead of querying it over and over

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 through the HTML page before JS can access anything

Question 11

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

Answer 11

a string with a CSS selector, returns first element that matches

Question 12

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

Answer 12

a string with a CSS selector, returns all elements that match

Question 13

What is the purpose of events and event handling?

Answer 13

makes a page more interactive and dynamic

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 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

event, an object created by the browser

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

where the event originated from, console.log to check, more info from mdn

Question 19

What is the difference between these two snippets of code?

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

Answer 19

the second one will call the function as soon as the page loads

Question 20

What is the className property of element objects?

Answer 20

it gets and sets the value of the class attribute of an element

Question 21

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

Answer 21

.className = ‘new-class’

Question 22

What is the textContent property of element objects?

Answer 22

it 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

.textContent = ‘next text content’

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

more complicated, you'd have more lines of code to retrieve the number of times a button was clicked

Question 26

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

Answer 26

more accessible

Question 27

What event is fired when a user places their cursor in a form control?

Answer 27

focus

Question 28

What event is fired when a user's cursor leaves a form control?

Answer 28

blur

Question 29

What event is fired as a user changes the value of a form control?

Answer 29

input

Question 30

What event is fired when a user clicks the "submit" button within a ?

Answer 30

submit

Question 31

What does the event.preventDefault( ) method do?

Answer 31

stops the browser from automatically doing the default action for an event

Question 32

What does submitting a form without event.preventDefault( ) do?

Answer 32

the browser will automatically reload the page with the form's values in the URL

Question 33

What property of a form element object contains all of the form's controls?

Answer 33

.elements

Question 34

What property of form a control object gets and sets its value?

Answer 34

value

Question 35

What is one risk of writing a lot of code without checking to see if it works so far?

Answer 35

you could make a mistake and not know which line it starts from

Question 36

What is an advantage of having your console open when writing a JavaScript program?

Answer 36

you can check for logs that show the output of your code while you run it, or for any errors

Question 37

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

Answer 37

no, it just creates a node, it's not part of the DOM tree yet

Question 38

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

Answer 38

.appendChild( )

Question 39

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

Answer 39

name, value

Question 40

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

Answer 40

.createElement( ), .appendChild( )

Question 41

What is the textContent property of an element object for?

Answer 41

to get and set the text content of a node

Question 42

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

Answer 42

.className or .setAttribute( class, value )

Question 43

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

Answer 43

you don't have to repeat the steps of creating and adding elements, and you can pass in different data models

Question 44

What is the event.target?

Answer 44

where the event originated from

Question 45

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

Answer 45

bubbling, the event flows from child to parent elements

Question 46

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

Answer 46

.tagName ( )

Question 47

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

Answer 47

a CSS selector, the closest matching ancestor

Question 48

How can you remove an element from the DOM?

Answer 48

.remove ( )

Question 49

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 49

add the event listener to the parent element

Question 50

What is the affect of setting an element to display: none?

Answer 50

removes it from the document flow, doesn't show up in the browser

Question 51

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

Answer 51

CSS selector, returns a boolean

Question 52

How can you retrieve the value of an element's attribute?

Answer 52

.getAttribute( )

Question 53

At what steps of the solution would it be helpful to log things to the console?

Answer 53

every step

Question 54

If you were to add another tab and view to your HTML, but you didn't use event delegation, how would your JavaScript code be written instead?

Answer 54

you'd have to add an event listener on each tab

Question 55

If you didn't use a loop to conditionally show or hide the views in the page, how would your JavaScript code be written instead?

Answer 55

you'd have to write conditionals for each individual view