DOM (Document Object Model)

Question 1

What is a “model”?

Answer 1

A representation of an existing thing/concept

Question 2

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

Answer 2

The HTML document being loaded

Question 3

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

Answer 3

It is referring to the data type: object in JavaScript

Question 4

What is a DOM Tree?

Answer 4

An element and all of its configurations + its relationship with its siblings/parents represented in the DOM

Question 5

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

Answer 5

document.querySelector()
document.getElementById()

Question 6

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

Answer 6

doucment.querySelectorAll()

Question 7

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

Answer 7

To keep the location/reference point saved so one doesn’t have to search the DOM Tree for an element repeatedly

Question 8

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

Answer 8

console.dir()

Question 9

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

Answer 9

One has to allow the web page to fully load before trying to map it out with a DOM Tree

Question 10

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

Answer 10

It takes a CSS selector as an argument and returns the first element found with that selector.

Question 11

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

Answer 11

Uses a CSS Selector and returns all elements found with that selector in a Node List.

Question 12

Does assigning the return value of a DOM query actually assign that node to the variable?

Answer 12

No, it only saves the location of where that element is in the DOM Tree. (Tl;dr saves a reference point)

Question 13

What is the DOM?

Answer 13

It is a recreation of the HTML Document stored as a JavaScript Object which is modeling the content of the HTML Document

Question 14

What is the purpose of events and event handling?

Answer 14

To run a script whenever certain things happen within or to the browser.
It makes web pages more interactive for the user.

Question 15

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

Answer 15

No, many functions/methods have optional parameters that do not need to be passed through as arguments for the function/method to execute.

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('event', functionName [, Boolean]) -Boolean optional

Question 17

What is a callback function?

Answer 17

A function passed as an argument through another function

Question 18

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

Answer 18

An event object that describes the event that occurred

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

A reference to the object in which an event was fired. One can check it by logging it. You could get more information at target documentation

Question 20

What is the difference between these two snippets of code?

element.addEventListener('click', handleClick)
element.addEventListener('click', handleClick())

Answer 20

handleClick is run when the event fires, while handleClick() is run while the page loads

Question 21

What is the className property of element objects?

Answer 21

A property that has the value of the classes applied to the element object as a string

Question 22

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

Answer 22

Re-assign element.className

Question 23

What is the textContent property of element objects?

Answer 23

A property that has the value of the text content of the element object

Question 24

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

Answer 24

Re-assign element.textContent

Question 25

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

Answer 25

No, as sometimes we want code to run that doesn’t have any reference to the event that caused the code to run.

Question 26

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

Answer 26

It prevents one from having to re-query a document again in order to find/update a node.

Question 27

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

Answer 27

The ‘focus’ event is fired

Question 28

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

Answer 28

The ‘blur’ event is fired

Question 29

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

Answer 29

The ‘event.target.value’ event is fired

Question 30

What event is fired when a user clicks the “submit” button within a <form>?

Answer 30

The ‘submit’ event is fired

Question 31

What does the event.preventDefault() method do?

Answer 31

It prevents the default behavior of the event.

Question 32

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

Answer 32

in the case of forms it prevents data from being passed into the URL and the page refreshing

Question 33

What property of a form element object contains all of the form’s controls.

Answer 33

The elements property

Question 34

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

Answer 34

The elements.whateverName.value property
Example syntax: $contactForm.elements.name.value

Question 35

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

Answer 35

No, it only creates it in the DOM.

Question 36

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

Answer 36

appendChild(childname)

Question 37

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

Answer 37

element.setAttribute('attributeName', 'attributeValue')

Question 38

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

Answer 38

One would need to create the element in the dom and add whatever necessary text content then append that element as a child to a queried element on the page.

Question 39

What is the textContent property of an element object for?

Answer 39

It is used to get or set the textContent found within an element

Question 40

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

Answer 40

One can use element.setAttribute() or provide it as an optional argument when using createElement

Question 41

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

Answer 41

It can easily be scaled and reapplied elsewhere on the page.

Question 42

What is the event.target?

Answer 42

It is the element which the event originated from.

Question 43

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

Answer 43

Event bubbling, which is default to event listeners unless one adds an optional boolean as an argument.

Question 44

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

Answer 44

event.target.tagName

Question 45

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

Answer 45

It takes a string as an argument with the syntax of a CSS selector and returns the closest ancestor.

Question 46

How can you remove an element from the DOM?

Answer 46

element.remove()

Question 47

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 47

By taking advantage of the default behavior of event listeners: event bubbling. With event bubbling one can instead stick a listener on a parent element and target its children. (This is called event delegation)

Question 48

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

Answer 48

It takes a string following the format of a css selector and returns a boolean of true if the selector is found on that element and false if it is not.

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

By taking advantage of the default behavior of event listeners: event bubbling. With event bubbling, one can instead stick a listener on a parent element and target its children. (This is called event delegation)

Question 50

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

Answer 50

It takes a string following the syntax of a CSS selector and returns a boolean true if that selector is found on the element it is used on and false if it isn’t.

Question 51

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

Answer 51

element.getAttribute('example')

Question 52

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 52

One would have to add an event listener for each tab + view.