Basics

Core modules:

• http→ Launch a server and recieve requests
• https
• fs
• path
• os
• buffer (no need to import)

createServer

http.createServer, takes a callback function which gets two params request and response and returns a server. Server is an object with method listen.

Node lifecycle & Event loop

Entire node process uses only one loop. process.exit ends the loop (process is available as global object in your node script)

Requests and Responses

• How will node internally call req on data? If you do ctrl + c, cpp code will determine something has changed and clear the stack for end event methods before terminating, anyinfinite_loop here will keep the process waiting.

Request = {
	url: string;
	method: string | 'GET' | 'POST';
	headers: Object,
	on: (event, cb) => {
		if (event === 'data') {
			// what data has come from stream internally pass it to cb
			cb(dataServerGot)
		}
		if (event === )
	}
}
 
Response = {
	statusCode: Number,
	setHeader: (key, val) => {
	
	},
	write: (content: string) => {
	// append some content here
	},
	end: () => { 
	// will this call process exit?
	}
}

• How to parse the buffer data?
• Ans. Buffer.concat(contentChunkArr).toString()

fileSystem module

• our request is a stream.
• buffer is chunk of data that come together const fs = { writeFileSync: (filename, contentToWrite) ⇒ {

}, writeFile(filename, message, cbError) { // will write file really fail, guess can fail if the size is too large or message is empy or something // offloads the job to operating system } }

• task Q. How do write file sync execute asynchronously?
• task Ans. It blocks the main thread, synchronous function should only be used when debugging.

Single thread, Event loop and Blocking code

• Q. How are multiple request processed if it issingle_threaded #worker_pool → does all heavy lifting. (handles multiple threads) Event loop is a loop which is keeps the process running and handles all callbacks.

1. First checks timers (setTimeout etc),
2. pending callbacks (execute)
3. Poll (retrieve new IO events, execute their callbacks) after can just to timers step 1
4. Check (execute setImmediate() callback)
5. close callbacks (all close event callbacks)
6. process.exit (if no remaining event handlers.) http.createServer is example of one event that keeps running and thus ref is never 0

Modules

module.exports = anyModuleName;
module.exports = {
	some: 'propHere',
	something: () => `I'm a method`
}
module.exports.someText = 'someText'

const routes = require('./routes')