DOM

Question 1

Why do we log things to the console?

Answer 1

to check and see if our output is what we expected.

Question 2

What is a “model”?

Answer 2

the structure of a web page.

Question 3

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

Answer 3

html.

Question 4

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

Answer 4

Data type object that can hold multiple values.

Question 5

What is a DOM Tree?

Answer 5

a model of a page. JavaScript object model of the html document. not the original, representation of the original. DOM is not html doc. JavaScript object recreating html document. javascript object for html element, including all of its attributes values and children’s attributes and values..

Question 6

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

Answer 6

querySelector, getElementById

Question 7

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

Answer 7

getElementsByClassName, getElementsByTagName, querySelectorAll

Question 8

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

Answer 8

so that you can access it and reuse it later.

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

you need the html document to load first before JavaScript does.

Question 11

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

Answer 11

takes string that contains css selector as argument and returns the first of the matching elements.

Question 12

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

Answer 12

takes string that contains css selector as argument and returns all of the elements that match as NodeList.

Question 13

Why do we log things to the console?

Answer 13

to check our work and see if the output is the result anticipated.

Question 14

What is the purpose of events and event handling?

Answer 14

events occur based on user interaction and makes website more interactive. Event handlers specify the type of user interaction. create a reaction, do that reaction in response to something happening. for interactivity in web applications.

Question 15

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

Answer 15

no. for instance, the splice method does not require new items to add in.

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 of element objects.

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. the code that you want it to run when the event fires. function definition being passes around as a value. there will never be a return value for a callback function.

Question 18

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

Answer 18

object with a huge amount of properties that contain all the data describing that event.

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 target property of the Event interface is a reference to the object onto which the event was dispatched. Where the event occurred. element where the event occurred.

Question 20

What is the difference between these two snippets of code?

Answer 20

One is a regular function calling expression, other is a callback function. In callback functions, parenthesis is omitted to indicate that the function should run as the page loads rather than when the event fires. one is passing function as an argument, other is assigning return value of a function.

Question 21

What is the className property of element objects?

Answer 21

sets the value of the class attribute of the specified element. property that hold value of class attribute for html element, and you can get that value or set that value.

Question 22

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

Answer 22

using className property and assigning new class name.

Question 23

What is the textContent property of element objects?

Answer 23

represents the text content of the node and its descendants.

Question 24

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

Answer 24

using textContent property and assigning new text content.

Question 25

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

Answer 25

no. you dont always need to know where the event happened. event object are very verbose, but not a guarantee that you need all the info. always have event parameter for call back functions to know that function is a event call back function

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

complicated

Question 27

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

Answer 27

because you can use it or modify it later. dont mix up html with javascript.

Question 28

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

Answer 28

no, just creates it

Question 29

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

Answer 29

appendChild method, append. append can receive multiple arguments, appendChild does not.

Question 30

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

Answer 30

attribute name, and the value for that attribute, in parenthesis.

Question 31

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

Answer 31

createElement, store new element, query for parent element, call appendChild on the parent with the new created element as an argument.

Question 32

What is the textContent property of an element object for?

Answer 32

represents the text content of the node and its descendants. retrieve text content or update text content if necessary.

Question 33

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

Answer 33

className property and setattribute method.

Question 34

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

Answer 34

you can call that function whenever you need that DOM Tree, you can pass in a parameter, which can be useful when structuring a DOM Tree. Give that function a name that clearly states what it does. easier to test.

Question 35

What is the event.target?

Answer 35

target property of event object, in which it shows the element where an event happened.

Question 36

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

Answer 36

because of event bubbling. if event occurs on one element, it also occurs on its parent elements.

Question 37

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

Answer 37

tagName property

Question 38

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

Answer 38

takes css selector as argument and returns matching ancestor.

Question 39

How can you remove an element from the DOM?

Answer 39

remove method.

Question 40

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 40

add the event listener on the parent of all those elements. you need to check if the event.target is the right place you want it to be.