Simple nested callback example

app.js

var express = require('express');
var request = require('request');
var app     = module.exports = express();

app.configure(function() {
  app.use(express.bodyParser());
  app.use(express.methodOverride());
  app.use(app.router);
});

app.post('/in', function(req, res) {
  
  // we are going to take the body from the post and 
  // forward it to the endpoint
  request.post({url: 'http://some.endpoint.com', body: req.body}, function(err, res, body) {
    
    // now we will respond to the client in the callback
    // from the request to the external endpoint.
    if(err) {
      // just forward the error back to the client when there is an error
      // from the endpoint
      res.send(err);
    } else {
      // send the body that we get in the callback on success
      res.send(body);
    }

  });

});