JavaScript DOM

Question 1

Why do we log things to the console?

Answer 1

Be aware of what we are doing, in DOM querys to make sure you know what element is selected.

Question 2

What is a “model”?

Answer 2

Its a recreation

Question 3

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

Answer 3

The HTML document we are working with.

Question 4

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

Answer 4

All the elements which are objects

Question 5

What is a DOM Tree?

Answer 5

A collection of all elements of the DOM

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 reuse an element quicker

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 HTML needs to be loaded (parsed) first so we can search for HTML elements.

Question 11

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

Answer 11

It takes a CSS-selector as a string. returns the first match

Question 12

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

Answer 12

Takes a CSS-selector.
Returns a node list of all elements that match.

Question 13

Why do we log things to the console?

Answer 13

So we know where we make errors and bugs, and dont have to search a page of code.

Question 14

What is the purpose of events and event handling?

Answer 14

Events and event handling allow us to make pages interactive.

Question 15

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

Answer 15

No. there are many optional parameters.

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

the addeventlistener method.

Question 17

What is a callback function?

Answer 17

a function being called that is declared outside the current function.

Question 18

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

Answer 18

The listener object generally a function

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

The event.target shows us what the event fired on ie. what button was clicked. and you can and should console log it while building your handlers.

Question 20

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

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

Answer 20

One is passing the function as a parameter and the other called the function and passes the result as the parameter.

Question 21

What is the className property of element objects?

Answer 21

it accessing the class atributes of the element

Question 22

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

Answer 22

with element.className = new class name

Question 23

What is the textContent property of element objects?

Answer 23

it is all the text

Question 24

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

Answer 24

with the el.textContent property

Question 25

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

Answer 25

Not always needed

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

Much more complicated.

Question 27

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

Answer 27

Faster and easier to retrieve information

Question 28

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

Answer 28

Focus event

Question 29

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

Answer 29

Blur event

Question 30

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

Answer 30

Input event

Question 31

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

Answer 31

submit event!

Question 32

What does the event.preventDefault() method do?

Answer 32

prevents the regular actions of the event if it is not being explicitly handled.

Question 33

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

Answer 33

The page will refresh.

Question 34

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

Answer 34

the elements collection.

Question 35

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

Answer 35

the name property.

Question 36

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

Answer 36

You won’t always know at which step your bug is coming from and may have to start from scratch.

Question 37

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

Answer 37

You can know exactly what each line of codes value is by logging it and seeing what changes.

Question 38

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

Answer 38

No, it just creates it separate of the dom tree.

Question 39

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

Answer 39

with the appendChild method

Question 40

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

Answer 40

(attribute, value)
i.e (‘class’, ‘container’)

Question 41

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

Answer 41

You have to create it then
You have to append the element as a child to an already existing element.
if there was not one, append to the body.

Question 42

What is the textContent property of an element object for?

Answer 42

this is how you can insert a text value to an element.
textContent is a getter, setter, can retrieve or change.

Question 43

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

Answer 43

You can use the attribute property or the className property and the classList property.

Question 44

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

Answer 44

Allows you to dynamically change your page content through user input, and allows you to import content from other pages.
Reusable!

Question 45

What is the event.target?

Answer 45

The event target references what element was interacted with.

Question 46

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

Answer 46

Event bubbling capturing it on the way up the dom tree.

Question 47

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

Answer 47

tagName property

Question 48

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

Answer 48

takes a css selector and returns the first matching ancestor

Question 49

How can you remove an element from the DOM?

Answer 49

element.remove

Question 50

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 50

Add an event listener for
for ancestors to capture all clickable descendants.

Question 51

What is the event.target?

Answer 51

The event target references what element was interacted with.

Question 52

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

Answer 52

It removes the element from the page

Question 53

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

Answer 53

it takes a css selector and returns true or false if it is present.

Question 54

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

Answer 54

getAttribute() method of the element.

Question 55

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

Answer 55

every variable, and every conditional statement, everytime you change something (though you can see changes in the html when adding or removing classes)

Question 56

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 56

You would have to add a listener to each tab.

Question 57

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 57

Using if elses or maybe a switch.

Question 58

What is a breakpoint in responsive Web design?

Answer 58

wheen we want a media rule to kick in.

Question 59

What is the advantage of using a percentage (e.g. 50%) width instead of a fixed (e.g. px) width for a “column” class in a responsive layout?

Answer 59

IT allows us to scale with screen size.

Question 60

If you introduce CSS rules for a smaller min-width after the styles for a larger min-width in your style sheet, the CSS rules for the smaller min-width will “win”. Why is that?