Exam

Question 1

What is the DOM?

Answer 1

Interface of a web app

Question 2

What is diffing?

Answer 2

Comparing the virtual DOMs for differences and re-rendering the real DOM with only these changes

Question 3

Why does React use virtual DOMs?

Answer 3

Speed

Question 4

What protocol does socket.io use?

Answer 4

Engine.IO

Question 5

What kind of connection does socket.io try first?

Answer 5

Websocket

Question 6

What kind of connection does socket.io use as a backup?

Answer 6

HTTP Long Polling

Question 7

In socket.io, what is the server instance called?

Answer 7

io

Question 8

Why did we use Express instead of Fastify?

Answer 8

Fastify is better for API calls, but in Case 2 we didn’t make any

Question 9

What was imported from socket.io on the server side?

Answer 9

Server

Question 10

How do you initialize the server instance?

Answer 10

const io = new Server( httpServer, { } ) ;

Question 11

What was installed for the client side of socket.io?

Answer 11

socket.io-client

Question 12

How do you initialize the socket instance on the client side?

Answer 12

const socket = io.connect(“localhost:5000”, { options });

Question 13

What function sets up a listener in socket.io?

Answer 13

on(“name”, listener())

Question 14

How do you send a message to the joining client from the server?

Answer 14

socket.emit(“funcName”, “message”)

Question 15

How do you send a message to the rest of the room from the server when a client first joins?

Answer 15

socket.to(“room”).emit(“funcName”, “message”)

Question 16

How do you get the number of clients in a room?

Answer 16

io.sockets.adapter.rooms.get(roomName).size

Question 17

How do you test if the server is trying to connect on the client side?

Answer 17

socket.io._readystate === “opening”

Question 18

How do you test if the client has failed to connect to the server?

Answer 18

socket.io._readystate === “closed”

Question 19

What is the private property that every JavaScript object has that points to a second object?

Answer 19

Prototype

Question 20

A new instance of Number inherits from which prototype?

Answer 20

Number.prototype and Object.prototype

Question 21

What is the hierarchy of prototypes called?

Answer 21

Prototype Chain

Question 22

Nearly all of JavaScript’s built-in constructors inherit from what?

Answer 22

Object.prototype

Question 23

What is the prototype chain used for?

Answer 23

If a property isn’t one of the object’s own properties the prototype chain will be checked for the property

Question 24

What does Object.create() do?

Answer 24

Creates an object using the prototype of the first argument

Question 25

What is the difference when connecting to socket.io server from the client when on the EBS?

Answer 25

The connect function is passed no arguments
io.connect()

Question 26

What does Math.floor() do?

Answer 26

Rounds a number DOWN to the nearest integer

Question 27

What does Math.random() return?

Answer 27

Random floating number between [0, 1)

Question 28

What 3 event handlers were needed for someone joining the server in Case 2?

Answer 28

1. nameexists
2. welcome
3. someonejoined

Question 29

What listener on the server side handles when a client disconnects?

Answer 29

socket.on(“disconnect”, …)

Question 30

What is Moment.js used for?

Answer 30

Handling date and times

Question 31

How do you format a date with Moment?

Answer 31

moment().format(‘date format’)

Question 32

How do you broadcast a message to everyone in the room including the sender?

Answer 32

io.in(roomName).emit(“funcName”, “message”)

Question 33

What property is used to handle pressing enter to send a message in Case 2?

Answer 33

onKeyPress={ }

Question 34

Why is the useRef hook used in Case 2?

Answer 34

scrollIntoView property

Question 35

The TopBar component uses what Material UI component?

Answer 35

Toolbar

Question 36

What is the TopBar button made of?

Answer 36

IconButton and SVG icon

Question 37

What triggers a Dialog component to show?

Answer 37

open={ }

Question 38

How do you set the timezone in app.js for Case 2?

Answer 38

process.env.TZ = “America/New_York”

Question 39

PWA

Answer 39

Progressive Web Apps

Question 40

What is a PWA?

Answer 40

Blends features of a native app and a website

Question 41

What is the key difference between PWA and a native app?

Answer 41

PWA runs in the browser

Question 42

PWAs are Really Fucking Exciting

Answer 42

Reliable
Fast
Engaging

Question 43

Why are PWA considered reliable?

Answer 43

Immediately loads and never shows website is down

Question 44

Where does the developer put all the metadata for a PWA?

Answer 44

Manifest

Question 45

What allows a PWA to allow for offline browsing, caching, background sync and push notifications?

Answer 45

Service Workers

Question 46

What kind of icon was used for the PWA?

Answer 46

Maskable Icon

Question 47

Where do you reference the manifest?

Answer 47

index.html

Question 48

Where is the service worker code that gets registered?

Answer 48

sw.js

Question 49

What are the 4 states of a service worker?

Answer 49

1. Installing
2. Activated
3. Idle
4. Fetch/Message

Question 50

If the PWA is offline in what is returned from the service worker fetch?

Answer 50

offline.html

Question 51

Where do you see the service worker?

Answer 51

Application tab in browser

Question 52

Where do you go to get an audit of your PWA?

Answer 52

Lighthouse