Simple node.js app that transforms a pages content using streams. Uses npm request and npm express. http://localhost:3000/replace?url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions&match=Regular

node-stream-transform.js

var express = require('express');
var app = express();
 
app.get('/replace', function(req, res) {
  var request = require('request');
  var stream = require('stream');
  var zlib = require('zlib');
 
 
  var url = req.query.url;
  var match = req.query.match;
 
  console.log("Calling url " + url + " and matching " + match);
 
  var Transform = require('stream').Transform;
 
  var replacer = new Transform();
  replacer._transform = function(chunk, encoding, done) {
    var data = chunk.toString();
 
    data = data.replace(new RegExp(match, 'g'),'MATCHED');
    console.log("replacing some stuff");
    this.push(data);
    done();
  }
 
  res.setHeader('Content-Type', 'text/html');
  req.pipe(request(url)).pipe(zlib.createGunzip()).pipe(replacer).pipe(res);
}).listen(3000);
console.log("Listening on 3000");