Node.js code to proxy an upstream webpage using cheerio

proxy.js

var http = require('http');
var express = require('express');
var router = express.Router();

/* GET users listing. */
router.get('/', function(req, res) {
  var request = require('request');

  var url = req.query.url;

  // If our URL doesn't contain a protocol or
  // ending slash, add it here
  if (url.indexOf('://') === -1) {
    url = 'http://' + url;
    if (!url.match(/\/$/)) {
      url += '/';
    }
  }

  var page = request.get(url, function(error, response, body) {
    if (!error) {
      var proxied = proxy(body, url);
      res.header('Cache-Control', 'no-cache, private, no-store, must-revalidate, max-stale=0, post-check=0, pre-check=0');
      res.send(proxied);
    }
  });
});

function proxy(html, url) {
  var cheerio = require('cheerio');
  var $ = cheerio.load(html);
  var content = '';

  var base = '<base href=\'' + url + '\' />\n';
  $('head').append(base);

  $('img[src^="public"]').each(function() {
    $(this).attr('href', url + '/' + $(this).attr('href'));
  });

  $('a:not([href^="http://"])' +
    ':not([href^="https://"])' +
    ':not([href^="//"])' +
    ':not([href^="javascript:"])')
    .each(function() {
      $(this).attr('href', url + $(this).attr('href'));
  });

  $('img:not([src^="http://"])' +
    ':not([src^="https://"])' +
    ':not([src^="//"])')
    .each(function() {
      $(this).attr('src', url + $(this).attr('src'));
  });

  $('link:not([href^="http://"])' +
    ':not([href^="https://"])' +
    ':not([href^="//"])')
    .each(function() {
      $(this).attr('href', url + $(this).attr('href'));
  });

  $('script[src]:not([src^="http://"])' +
    ':not([src^="https://"])' +
    ':not([src^="//"])')
    .each(function() {
      $(this).attr('src', url + $(this).attr('src'));
    });


  if (process.env.NODE_ENV === 'production') {
    var mavenjs = '<script id="prod"></script>\n';
    $('a').each(function() {
      $(this).attr('href', 'http://example.com/proxy?url=' + $(this).attr('href'));
    });
  }

  if (process.env.NODE_ENV === 'development') {
    var mavenjs = '<script id="dev"></script>\n';
    $('a').each(function() {
      $(this).attr('href', 'http://localhost:3000/proxy?url=' + $(this).attr('href'));
    });
  }

  $('body').append(mavenjs);

  return $.html();
};

module.exports = router;

This code doesn't include the routes or surrounding Express code. Use with caution as it may not suit your requirements.

This looks pretty great!