How to pipe to function in node.js?

Question

I want to read from file to stream, pipe the output to a function that will upperCase the content and then write to file. This is my attempt. What am I doing wrong?

Answer 1

Based on answer from Marco but tidied up:

const fs = require('fs')
const {Transform} = require('stream')

const upperCaseTransform = new Transform({
    transform: (chunk, encoding, done) => {
        const result = chunk.toString().toUpperCase()
        done(null, result)
    }
})

fs.createReadStream('input.txt')
    .pipe(upperCaseTransform)
    .pipe(fs.createWriteStream('output.txt'))