4 Fundamental Stream Types.

In Simple Words:

1. Readable: Source of data (fs.createReadStream, HTTP request).
2. Writable: Destination for data (fs.createWriteStream, HTTP response).
3. Duplex: Both Readable and Writable (e.g., net.Socket).
4. Transform: Duplex stream that modifies or transforms data while reading and writing (e.g., zlib.createGzip()).

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

// Transform stream that converts chunks to uppercase:
const upperCaseStream = new Transform({
  transform(chunk, encoding, callback) {
    callback(null, chunk.toString().toUpperCase());
  }
});