console.log("welcome world of backend")
const os = require('os')
// console.log(os.cpus())
console.log(os.uptime())
to read a file by using readFile
const { error } = require('console')
const fs = require('fs')
fs.readFile('./sample.txt','utf-8',(error, data)=>{
 if(error){
 console.log(error)
 }
 else{
 console.log(data)
 }
})
Using readFileSync method // comparing to both this exceute fast because O(n)
let data = fs.readFileSync('./sample.txt','utf-8')
console.log('sync',data)
To write a new file => fs.writeFile('path','data','formate(utf-8)',(error)=>{ if (error) console.log(error) else console.log('File created success')})
fs.writeFile('./sampleForWriteFile.txt','Hai we created a new file','utf-8',(error)=>{
 if(error)
 console.log(error)
 else
 console.log('File created Successfully')
})
To write and read a sync method
To write
fs.writeFileSync('./sampleSync.txt','This is a sync method','utf-8')
let syncdata = fs.readFileSync('./sampleSync.txt','utf-8')
To create a server 
const http = require('http')
const server = http.createServer((req,res)=>{
 res.writeHead(200,{
 "content-type":"text/html"
 })
 res.end(`<h1>Hello Server Is runing</h1>`)
})
server.listen(8000,()=>"server is running in 8000")
TO create a json
const http = require('http')
const server = http.createServer((req,res)=>{
 res.writeHead(200,{
 "content-type":"application/json"
 })
 res.end(JSON.stringify({
 name:"anbu",
 email:"anbu@gmail.com"
 }))
})
server.listen(8000,()=>console.log("server is lisning port 8000"))
To write a file and read to listen the port 
const fs = require('fs')
const http = require('http')
let time = new Date().toLocaleString()
const server = http.createServer((req,res)=>{
 try {
 fs.writeFileSync('./date.txt',`${time}`,'utf-8')
 let data = fs.readFileSync('./date.txt','utf-8')
 res.writeHead(200,{
 "content-type":"text/html"
 
 })
 res.end(`${data}`)
 } catch (error) {
 console.log(error)
 } 
})
server.listen(8000,()=>console.log("server is lisning port 8000"))