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

You have to use Transform if you want to "transform" streams. I recommend you to read: https://community.risingstack.com/the-definitive-guide-to-object-streams-in-node-js/

const fs = require('fs')

const Transform = require('stream').Transform;

  /// Create the transform stream:
  var uppercase = new Transform({
    decodeStrings: false
  });

  uppercase._transform = function(chunk, encoding, done) {
    done(null, chunk.toString().toUpperCase());
  };

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

EDIT: You need to call .toString() in chunk because it's a buffer! :)