Duplex Stream with Node.js

throttle.js

const { PassThrough, Duplex } = require("stream");
const { createReadStream, createWriteStream } = require("fs");

const readStream = createReadStream("../../powder-day.mp4");
const writeStream = createWriteStream("./copy.mp4");

class Throttle extends Duplex {
  constructor(ms) {
    super();
    this.delay = ms;
  }

  _write(chunk, encoding, callback) {
    this.push(chunk);
    setTimeout(callback, this.delay);
  }

  _read() {}
  _final() {
    this.push(null);
  }
}

const report = new PassThrough();

const throttle = new Throttle(10);

let total = 0;

report.on("data", chunk => {
  total += chunk.length;
  console.log("bytes: ", total);
});

readStream
  .pipe(throttle)
  .pipe(report)
  .pipe(writeStream);