Code for blog post at http://spiechu.pl/2017/01/01/serving-throttled-static-files-in-nodejs-express/

app.js

const express = require('express');
const app = express();

// define app logging, middleware, view engine etc.

// make sure you
// npm install advanced-throttle --save
const Throttle = require('advanced-throttle');

// boring factory...
const createThrottle = function () {
    // max transfer 5000 bytes / second
    return new Throttle(5000);
};

// we're going to serve files on '/public' dir
const serveStatic = express.static(path.join(__dirname, 'public'), {});

// typical Express middleware
app.use('/public', function (req, res, next) {
    // stream emits 'pipe' event when piped
    res.on('pipe', function (readStream) {
        // protects against infinite loop
        if (readStream instanceof Throttle) {
            return;
        }
      
        // first unpipe streams
        readStream.unpipe(res);

        // then reattach with Transform type between streams
        // Throttle class extends require('stream').Transform
        readStream.pipe(createThrottle()).pipe(res);
    });

    // start serving files
    serveStatic(req, res, next);
});