DOM

Question 1

Why do we log things to the console?

Answer 1

to spot check that our code works and debug it, verification, landmark to see code execute.

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. the entire page.

Question 4

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

Answer 4

refers to the data type object within javascript.

Question 5

What is a DOM Tree?

Answer 5

an element plus all of its children and their configuration.

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

to store the reference/location of the object in the DOM tree (caching). it saves the browser looking through the DOM tree to find the same element again.

Question 9

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

Answer 9

console.dir(object)

Question 10

Why would a

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

Answer 10

it speeds up page load times by loading the HTML content first before running DOM scripts.

Question 11

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

Answer 11

it takes CSS selectors as a string as its argument and returns the first matching element.

Question 12

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

Answer 12

it takes CSS selectors as a string as its argument and returns a nodelist of all the elements.

Question 13

What is the purpose of events and event handling?

Answer 13

to prepare to trigger a function and make the website more interactive

Question 14

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

Answer 14

No, there are optional parameters.

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, which is then invoked inside the outer function to complete some kind of routine or action

Question 17

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

Answer 17

information about what happens.

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

it holds the element where the information originated from. you can check with console log and find more information on MDN.

Question 19

What is the difference between these two snippets of code?
element.addEventListener(‘click’, handleClick)
element.addEventListener(‘click’, handleClick())

Answer 19

the parentheses are omitted. parentheses indicate that the function should run as the page loads rather than when the event fires.

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

element.className = ‘new class name’

Question 22

What is the textContent property of element objects?

Answer 22

allows you to collect or update just the text in its containing element

Question 23

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

Answer 23

element.textContent = ‘new text’

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

Question 26

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

Answer 26

By keeping data in javascript you don’t make your data dependent on another language in the DOM.

Question 27

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

Answer 27

No. it is stored in a variable until attached to DOM tree later with appendChild.

Question 28

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

Answer 28

appendChild()

Question 29

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

Answer 29

name (of attribute) and value

Question 30

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

Answer 30

create element, store in a variable, DOM query, appendChild

Question 31

What is the textContent property of an element object for?

Answer 31

it 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

setAttribute() and .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

You can reuse it later on without having to create a new DOM tree.

you can give it the function a name so it’s easier to track.

Question 34

What is the event.target?

Answer 34

it holds the element where the information originated from

Question 35

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

Answer 35

Event bubbling flow.

Question 36

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

Answer 36

event.target.tagName … tagName is in all caps.

Question 37

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

Answer 37

selectors - a string of a valid CSS selector
returns the closest ancestor element or itself, which matches the selectors. If none, returns null.

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

By adding the event listener to an ancestor element.

Question 40

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

Answer 40

it removes the element from the document flow.

Question 41

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

Answer 41

selectors (a string containing valid CSS selectors) to test against element

returns true if element matches selector, false otherwise

Question 42

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

Answer 42

getAttribute()

Question 43

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

Answer 43

every step

Question 44

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 44

It would have to have a function and event listener for each tab and view

Question 45

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 45

you would have to write a function and event listener for each tab and view and have a conditional statement for each function to hide the other tabs.