index.js

// const file = require('./file.csv')
import { readFile, createReadStream} from 'node:fs'
import readline from 'node:readline'

const old = () => {
  console.time()
  readFile('file.csv', 'utf-8', (err, data) => {
    // console.log(data)
    console.timeEnd()
  })
}

// default: 1.691s
const newLine = () => {
  console.time()
  const readable =  createReadStream('file.csv')
  
  const rl = readline.createInterface({
    input: readable,
    // Note: we use the crlfDelay option to recognize all instances of CR LF
    // ('\r\n') in input.txt as a single line break.
    crlfDelay: Infinity,
  })

  rl.on('line', (line) => {
    // console.log(`Line from file: ${line}`);
  })

  rl.on('close', () => {
    console.log('finished!')
    console.timeEnd()
  })
}

// default: 3.872s ==> 978.47ms Utilizando los slice.
const newV = () => {
  console.time()
  const readable =  createReadStream('file.csv', { highWaterMark: 20 })
  
  let newLineI = '' 
  let newLine = ''
   
  readable.on('data', chunk => {
    // console.log({data: chunk.toString()})

    const chunky =  chunk.toString()
       
    let indexSlice = 0
    for(let i = 0; i < chunky.length; i++){
      if(chunky[i] === '\n'){

        newLine += chunky.slice(indexSlice, i)
        // newLine += chunky[i]
        console.log(newLine)
        newLine = ''
        indexSlice = i
      } 
      // else {
      //   newLine += chunky[i]
      // }
    }
  })

  readable.on('end', () => {
    console.log('finished!')
    console.timeEnd()
  })
}

// old()
newV()
// newLine()