DOM

Question 1

Why do we log things to the console?

Answer 1

It is a way to debug scripts and make sure scripts are running smoothly

So we can look at what we are working with

Question 2

What is a “model”?

Answer 2

It is an imitation of something else

Question 3

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

Answer 3

HTML code

Question 4

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

Answer 4

Data type object

Question 5

What is a DOM Tree?

Answer 5

A parent element and all of its child elements

As a browser loads a web page, it creates a model of that page. The model is called a DOM tree, and it is stored in the browsers’ memory.

It consists of 4 types of nodes:	
Document node
Element node
Attribute node
Text Nodes

Question 6

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

Answer 6

getElementById()

querySelector() - uses a CSS selector, and returns the first matching object - only one we need

Question 7

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

Answer 7

getElementByClassName()

getElementByTagName()

querySelectorAll() -only one to use

Question 8

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

Answer 8

It is easier to re-use that element

Saves the browser looking through the DOM tree to find the same elements again. It is known as caching the selection

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

The browser needs to parse all of the elements in 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

returns the first Element within the document that matches the specified selector, or group of selectors. If no matches are found, null is returned.

Question 12

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

Answer 12

Returns the node list of all elements

Node list is not an array

Question 13

Why do we log things to the console?

Answer 13

It is a way to debug scripts and make sure scripts are running smoothly

So we can look at what we are working with

Question 14

What is the purpose of events and event handling?

Answer 14

Allows users to interact with the page

Our way to respond to things happening

Question 15

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

Answer 15

no

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 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 18

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

Answer 18

Event object with all the info about 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

Property of the event object
Points to the element where the event occured
Checking mdn

Question 20

What is the className property of element objects?

Answer 20

The className property of the Element interface 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

First get the element using a method from the document object then you use the class name object and assign a new string to it

Question 22

What is the textContent property of element objects?

Answer 22

The textContent property of the Node interface 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

First get a specific element using a query selector method from the document object. Then use the .textContent method and assign a new string to it.

Question 24

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

Answer 24

Not always useful.

Helpful to know if we are looking at an event handler function

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 JavaScript functionality should rely on data that is stored in JavaScript

Question 26

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

Answer 26

It’s easier to work with if it is stored

Question 27

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

Answer 27

The ‘focus’ event | Returns the console log of the function handleFocus()

Question 28

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

Answer 28

The ‘blur’ event Returns the console logs within the handleBlur() function

Question 29

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

Answer 29

‘Input’ Returns the value of what is inside the form control

Question 30

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

Answer 30

The ‘submit’ event. It then calls the function created

Question 31

What does the event.preventDefault() method do?

Answer 31

Prevents the default action of the event An example is the form refreshing the page

Question 32

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

Answer 32

Without the event.preventDefault(), it clears all of the console.log

Question 33

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

Answer 33

.elements hold an object with a named property for each form control element

Question 34

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

Answer 34

.value the property on form control elements that allows you to access the 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 can write bad code without knowing its bad, and even build on that bad code

Question 36

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

Answer 36

You can check for mistakes and bugs as you are coding

Question 37

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

Answer 37

no

Question 38

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

Answer 38

.appendChild(element)

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

First create element using .createElement() Then .appendChild from the element object created

Question 41

What is the textContent property of an element object for?

Answer 41

It grabs the text from that element or it changes the text if you assign a string to it

Question 42

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

Answer 42

Element.setAttribute()

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 can reuse the function It can be done after the HTML has been created Makes a page interactive Easier to test because you can pass in whatever and test it that way

Question 44

What is the event.target?

Answer 44

Tells you what element you clicked on

Question 45

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

Answer 45

Due to event bubbling. Starts at a specific node and flows outwards

Question 46

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

Answer 46

element.target.tagName Elements have a tag name property and that tells you what property it is

Question 47

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

Answer 47

The selector of the direct parent Returns the closest ancestor

Question 48

How can you remove an element from the DOM?

Answer 48

Element.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 an event listener to the parent of the element and in the function have a conditional that triggers when the specific tagName is clicked

Question 50

What is the event.target?

Answer 50

event .target is where the event occurred, in this case, where it was clicked. It gives the entire element

JavaScript

The element that triggered the event

Question 51

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

Answer 51

Hides the content

Question 52

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

Answer 52

A string in the form of a css selector Returns a boolean

Question 53

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

Answer 53

element.getAttribute(‘string of attribute’) Returns value of attribute

Question 54

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

Answer 54

Every step

Question 55

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 55

You would have to use queryselector for a lot of elements

Question 56

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 56

Have a variable for each .tab class and .view class Have a bunch of if / if else statements