NodeJs

Question 1

CommonJS modules ( 3 characteristics)

Answer 1

Uses require and module.exports
Synchronous loading
Default in nodeJs

Question 2

ECMAScript Modules ( 3 characteristics)

Answer 2

Uses import and exports , standard JS
Asynchronous loading
Works in nodejs and browsers

Question 3

How to use ECMAScript modules

Answer 3

package.json = { “type”: “module” }

Question 4

Code to create a http server

Answer 4

import http from ‘http’
http.createServer( (req, res) => {})
server.listen( port, err => {})
res.writeHead( code, { “header”:”content”})
res.write(data);
res.end()

Question 5

fs (File System)

Answer 5

Handles file operations such as reading, writing and deleting files.
writeFileSync(name, text)
readFileSync( path,encoding)

Question 6

path

Answer 6

Helps with working with file and directory paths
path.join(_dirname, filename)

Question 7

https

Answer 7

Similar to http but handles htpps secure requests.
https.get( url, (res) => res.on())

Question 8

os

Answer 8

Provides OS related utilities
os.platform()
os.totalmem()
os.freemem()

Question 9

crypto

Answer 9

Provide cryptographic functions as hasing and encryption.
const hash = crypto.createHash(‘sha256’).update(‘password123’).digest(‘hex’);

Question 10

events

Answer 10

Implements an event-driven architecture using EventEmitter.
new EventEmitter();
emitter.on(‘event’, callback)
emitter.emit(‘event’)

Question 11

util

Answer 11

Provides utilities such as promistificattion of callback-based functions.

Question 12

child_process

Answer 12

Execute shell commands and external programs.
exec(‘ls’, (error,stdout, stderr) => {})

Question 13

stream

Answer 13

Handles streaming data, large files.
const readStream = fs.createReadStream(‘example.txt’, ‘utf-8’);
readStream.on(‘data’, chunk => console.log(chunk));

Question 14

3 Javascript Execution data

Answer 14

JS is synchronous
Js is blocking
Js is single-threated

Question 15

What is NodeJs Event Loop?

Answer 15

C program that coordinates the execution of code in Node.Js uses V8 engine and libuv library for sync and sync ops.

Question 16

How does V8 and libuv work?

Answer 16

V8 has the memory memory head and the call stack for sync ops, libuv works only when we have async functions

Question 17

What is libuv?

Answer 17

Libuv is a cross-platform open-source library written in C. In the Node.js runtime, its role is to provide support for handling asynchronous operations.

Question 18

Does Node wait for the call stack to be empty before running the callback function, or does it interrupt the normal flow of execution to run the callback function?

Answer 18

Node.js does NOT interrupt the normal flow of execution to run an asynchronous callback, it waits for the call stack to be empty.

Question 19

Is valid to use await at js top level file?

Answer 19

await at the top level is only valid in ES modules.

Question 20

What are the phases of the Event Loop?

Answer 20

1. Timers
2. I/O Poll
3. Check Queue
4. Close Queue

Question 21

What are microstasks in the Event Loop?

Answer 21

This tasks are process.NexThick or promises.resolve that get executed right away, without waiting for the next phase.

Question 22

Does Node wait for the call stack to be empty before running the callback function, or does it interrupt the normal flow of execution to run the callback function?

Answer 22

Node.js does NOT interrupt the normal flow of execution to run an asynchronous callback, it waits for the call stack to be empty

Question 23

If two async tasks such as setTimeout and readFile complete at the same time, how does Node decide which callback function to run first on the call stack? Does one get priority over the other?

Answer 23

Timer callbacks are executed before I/O callbacks, even if both are ready at the exact same time.

Question 24

What are I/O ops?

Answer 24

Input Output ops.
Http Requests, Reading from a File, sockets