stream-class.js

var { Transform } = require('stream');  // use require for non-ES6 Node modules

class MyStream extends Transform {
  constructor (options) {
    super({
      lowWaterMark: 0,
      encoding: 'utf8'
    });
  }

  _transform(chunk, encoding, cb) {
    this.push(String(chunk).toUpperCase());
    cb();
  }

}