WebSockets Quiz

To pass the quiz, you must correctly answer at least 18 of the 20 questions below. # --quizzes-- ## --quiz-- ### --question-- #### --text-- Why does Node.js require an external library for WebSocket servers? #### --distractors-- Node.js has a built-in WebSocket server but it requires extra configuration to enable. --- Node.js only supports WebSockets when using the Express framework. --- Node.js cannot support WebSockets at all, regardless of external packages. #### --answer-- Node.js does not have a built-in WebSocket server. ### --question-- #### --text-- What are the three main parts of a Pub/Sub architecture? #### --distractors-- Senders, queues, and receivers. --- Producers, channels, and consumers. --- Clients, servers, and databases. #### --answer-- Publishers, topics, and subscribers. ### --question-- #### --text-- What communication model does HTTP follow? #### --distractors-- A persistent bidirectional model. --- A broadcast model. --- A pub/sub model. #### --answer-- The request-response model. ### --question-- #### --text-- Which WebSocket event fires when a new client connects to the server? #### --distractors-- `connect` --- `open` --- `join` #### --answer-- `connection` ### --question-- #### --text-- What is the main disadvantage of direct application-to-application communication compared to Pub/Sub? #### --distractors-- Direct communication is always slower than Pub/Sub. --- Direct communication prevents applications from sending more than one message. --- Direct communication always requires a third-party authentication server. #### --answer-- It creates an unnecessary dependency between the applications; a change or failure in one app can break the other. ### --question-- #### --text-- Which protocol does a WebSocket connection start with before upgrading? #### --distractors-- WebSocket connections start with a dedicated WebSocket protocol from the very beginning. --- WebSocket connections start with TCP, bypassing HTTP entirely. --- Every WebSocket connection starts with FTP, then upgrades to WebSocket. #### --answer-- Every WebSocket connection begins with HTTP. ### --question-- #### --text-- What method do you call to send data through a WebSocket connection to a client? #### --distractors-- `socket.emit()` --- `socket.write()` --- `socket.push()` #### --answer-- `socket.send()` ### --question-- #### --text-- What role does a topic play in a Pub/Sub system? #### --distractors-- It stores messages permanently for future retrieval. --- It authenticates publishers before they can send messages. --- It directly connects publishers to specific subscribers. #### --answer-- It acts as the middleman between publishers and subscribers. ### --question-- #### --text-- How does HTTP communication differ from WebSocket communication? #### --distractors-- HTTP is bidirectional while WebSocket is unidirectional. --- HTTP keeps a permanent connection, while WebSocket closes after each exchange. --- HTTP and WebSocket both follow the same request-response pattern. #### --answer-- HTTP follows `Client --> Request --> Server --> Response`, while WebSocket is `Client <--> Server`. ### --question-- #### --text-- Why should you check `client.readyState === WebSocket.OPEN` before broadcasting to connected clients? #### --distractors-- To encrypt the message before sending it to each client. --- To limit the number of messages sent per second to each client. --- To verify the client has permission to receive the message. #### --answer-- To avoid errors when sending to clients that have disconnected or are still connecting. ### --question-- #### --text-- What HTTP status code does the server send when it accepts a WebSocket upgrade request? #### --distractors-- `200 OK` --- `301 Moved Permanently` --- `426 Upgrade Required` #### --answer-- `101 Switching Protocols` ### --question-- #### --text-- Which of the following is a real-world use case for Pub/Sub? #### --distractors-- A static web page that loads HTML from a server. --- A command-line tool that processes files one at a time. --- A relational database that stores and queries structured data. #### --answer-- A notification system that delivers real-time alerts to all its subscribers. ### --question-- #### --text-- How do you create a WebSocket server on port `3000` using the `ws` library? #### --distractors-- ```js const server = new WebSocket({ port: 3000 }); ``` --- ```js const server = WebSocket.createServer(3000); ``` --- ```js const server = ws.listen(3000); ``` #### --answer-- ```js const server = new WebSocket.Server({ port: 3000 }); ``` ### --question-- #### --text-- Which WebSocket event is triggered when a connection closes? #### --distractors-- `disconnect` --- `end` --- `terminate` #### --answer-- `close` ### --question-- #### --text-- What is the Pub/Sub message flow? #### --distractors-- A publisher sends to a subscriber --> the subscriber forwards to a topic --> the topic stores the message. --- A topic sends a message --> publishers receive it --> publishers forward it to subscribers. --- A subscriber connects to a publisher --> the publisher sends data --> the subscriber acknowledges receipt. #### --answer-- A subscriber subscribes to a topic --> a publisher sends a message to that topic --> the messaging system delivers it to all subscribers of that topic. ### --question-- #### --text-- Which analogy best describes how HTTP and WebSockets differ? #### --distractors-- HTTP is like a phone call, and WebSockets are like exchanging letters. --- HTTP is like a chat room, and WebSockets are like a newspaper. --- HTTP is like a live stream, and WebSockets are like a stored video. #### --answer-- HTTP is like exchanging letters, and WebSockets are like a phone call. ### --question-- #### --text-- Which WebSocket event fires when a connected client sends data to the server? #### --distractors-- `data` --- `receive` --- `incoming` #### --answer-- `message` ### --question-- #### --text-- Which of the following correctly describes the WebSocket connection flow? #### --distractors-- Client connects via TCP --> server sends data --> client receives --> connection closes. --- Client sends data --> server requests upgrade --> connection opens --> client acknowledges. --- Server initiates a connection --> client accepts --> both sides exchange data --> connection closes. #### --answer-- Client connects via HTTP --> server responds with `101 Switching Protocols` --> connection stays open --> both sides exchange data at any time. ### --question-- #### --text-- How do WebSockets and Pub/Sub differ in a real-time application? #### --distractors-- WebSockets handle authentication while Pub/Sub handles data storage. --- WebSockets are for server-to-server communication while Pub/Sub is for client-to-server communication. --- They are the same technology with different names. #### --answer-- WebSockets provide the communication channel while Pub/Sub provides the messaging pattern. ### --question-- #### --text-- Which of the following is a real-world use case for WebSockets? #### --distractors-- A static blog page displaying articles. --- A server-side file rendering system. --- A database that stores user records. #### --answer-- A chat application.