A simple express.js server with a proxy that intercepts all requests with /api/ and proxies them to localhost:3000

api.proxy.server.js

var express   = require('express'),
    httpProxy = require('http-proxy'),
    app       = express();

var proxy = new httpProxy.RoutingProxy();

function apiProxy(host, port) {
  return function(req, res, next) {
    if(req.url.match(new RegExp('^\/api\/'))) {
      proxy.proxyRequest(req, res, {host: host, port: port});
    } else {
      next();
    }
  }
}

app.configure(function() {
  app.use(express.static(process.cwd() + "/generated"));
  app.use(apiProxy('localhost', 3000));
  app.use(express.bodyParser());
  app.use(express.errorHandler());
});

module.exports = app;

Thanks for your gist
Here is my update written in ES6 with new version of node proxy > https://gist.github.com/gouroujo/a5d7d5582128d099cbfc5e826c55e311

const proxy = require('express-http-proxy');

const getPath = req => require('url').parse(req.url).path;

const createProxy = ({hostname = 'localhost', port = 80, path = ''}) =>
+  proxy(`${hostname}:${port}`, { proxyReqPathResolver: req => `${path}${getPath(req)}` });

app.use('/api', createProxy({port: 3000, path: '/api'})); // http://localhost/api/foo -> http://localhost:3000/api/foo 

thanks @ajs139 🎉