THE DOM

Question 1

Why do we log things to the console?

Answer 1

To see a variable’s contents, to see what an element contains when using dom query commands.

Question 2

What is a “model”?

Answer 2

It is a representation of something else.

Question 3

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

Answer 3

The HTML document

Question 4

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

Answer 4

The model is made of objects, each object in the model represents a different part of the page in the browser window.

Question 5

What is a DOM Tree?

Answer 5

A DOM element and all of its DOM child elements and contents.

Question 6

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

Answer 6

document.querySelector(), document.getElementById()

Question 7

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

Answer 7

document.getElementByClassName(), document.getElementByTagName(), document.querySelectorAll().

Question 8

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

Answer 8

So you can keep track of an element Node’s location in order to use it multiple times without retrieving it again.

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 script 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 before interacting with them

Question 11

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

Answer 11

A css selector (tag name, class name, id name) it returns the location of the first of that matching element

Question 12

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

Answer 12

Css selector (tag name, class name, id name) and returns all of the elements that match in a node list

Question 13

What is the purpose of events and event handling?

Answer 13

Do react and trigger events when something is done by the user

Question 14

What do [] square brackets mean in function and method syntax documentation?

Answer 14

They are optional

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

It is 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

An event object with all of the info of that event.

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 is the target dom element that triggered the event. You can log the event and see the target element in the target property

Question 19

What is the difference between these two snippets of code?

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

Answer 19

With out parenthesis means that the function should be called when the event fires, with () means that that function should run as the page loads

Question 20

What is the className property of element objects?

Answer 20

It is a method that can be used to grab the class names of a dom element as a string, or be reassigned

Question 21

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

Answer 21

domelement.className = ‘className’. This rewrites the entire class attribute so if you are adding one class you need to re-add the other classes

Question 22

What is the textContent property of element objects?

Answer 22

It is a method that can be used to grab the text content of a dom element as a string, or be reassigned

Question 23

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

Answer 23

With .textContent

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 because we would have to retrieve it from the dom each time

Question 26

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

Answer 26

It is important because it is similar for the computer to access a variable with the value than pulling it from the dom each time.

Question 27

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

Answer 27

no

Question 28

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

Answer 28

Using the .appendChild method

Question 29

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

Answer 29

(‘attribute type’, ‘attribute value’)

Question 30

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

Answer 30

Create element node, create text node (if needed), set attributes (if needed), add text nodes and attributes, add to dom tree.

Question 31

What is the textContent property of an element object for?

Answer 31

To add text content to an element

Question 32

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

Answer 32

.setAttribute, .className, classList

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 replicate the same dom tree section and give it different values.

Question 34

What is the event.target?

Answer 34

The target is the element that the event was triggered from

Question 35

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

Answer 35

Because event flow bubbling

Question 36

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

Answer 36

event.target.tagName

Question 37

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

Answer 37

It takes a selector in string form and returns the element that is closest to the selector

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

You would add an event listener to the parent of the elements being added.