DOM

Question 1

Why do we log things to the console?

Answer 1

To double check the code is doing what is intended.

Question 2

What is a “model”?

Answer 2

The model is called a DOM tree. The tree is stored in the browsers’ memory.

Question 3

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

Answer 3

The document is the html file.

Question 4

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

Answer 4

The object represents a different object for each part of the page.

Question 5

What is a DOM Tree?

Answer 5

A model of the selected element.

Question 6

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

Answer 6

querySelector and getElementById

Question 7

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

Answer 7

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 have an access point instead of having to query it every time you need it.

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

So the js file can parse the entire html content first.

Question 11

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

Answer 11

querySelector takes css selectors and the argument and returns the content of that element.

Question 12

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

Answer 12

querySelectorAll takes css selectors and returns a node list.

Question 13

Why do we log things to the console?

Answer 13

To clearly see what our line of code is doing.

Question 14

What is the purpose of events and event handling?

Answer 14

Events are used to trigger a particular function. Event handlers are steps triggered after the event occurs.

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

object.addEventListener.

Question 16

What is a callback function?

Answer 16

A callback function is a function passed into another function as an argument. It invokes the function inside.

Question 17

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

Answer 17

The type of event, and the function given.

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

If not sure, console log the event.target. MDN has more information. Event.target is a DOM interface implemented by objects that can receive events and may have listeners for them.

Question 19

What is the difference between these two snippets of code?

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

Answer 19

The snippet with the callback function calls that line of code when its run instead of when the event occurs.

Question 20

What is the className property of element objects?

Answer 20

The className property allows us to get the value of the class attribute, as well as setting the value of it.

Question 21

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

Answer 21

You would query the element first and then use the className property to update the attribute.

Question 22

What is the textContent property of element objects?

Answer 22

The textContent property collects the text in that element as well as allowing updates to the text.

Question 23

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

Answer 23

Query the element first and then use textContent to update the text.

Question 24

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

Answer 24

No, but the event parameter should always be used.

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

Harder.

Question 26

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

Answer 26

With the variable, we can reuse that query. Without the variable, we would have to query the DOM every time.

Question 27

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

Answer 27

focus event

Question 28

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

Answer 28

blue event

Question 29

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

Answer 29

input event

Question 30

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

Answer 30

submit event

Question 31

What does the event.preventDefault() method do?

Answer 31

It tells the current event that is referred to, to not do the default behavior.

Question 32

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

Answer 32

The page will refresh and lose the submitted form because it has no where to store it.

Question 33

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

Answer 33

HTMLFormControlsCollection

Question 34

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

Answer 34

HTMLFormElement

Question 35

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

Answer 35

Waste of time. Hard to debug the longer it is.

Question 36

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

Answer 36

To constantly check if the js code is functional.

Question 37

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

Answer 37

yes

Question 38

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

Answer 38

element.appendChild(childelement)

Question 39

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

Answer 39

An attribute name as the first argument and a value for that attribute as the second argument.

Question 40

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

Answer 40

Use document.createElement() to make the element. Then add this newly created element to the desired parent element using element.appendChild()

Question 41

What is the textContent property of an element object for?

Answer 41

The textContent property gets text content of that element or to set the element’s text content.

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

To work with data that we don’t know the exact size of. It allows the code to be reusable.

Question 44

What is the event.target?

Answer 44

.

Question 45

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

Answer 45

.

Question 46

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

Answer 46

.

Question 47

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

Answer 47

.

Question 48

How can you remove an element from the DOM?

Answer 48

.

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

.