Simple example on using CartoDB.js with Express.

cartodb-express.js

// requirements
var carto   = require('cartodb'),
    express = require('express'),
    secret  = require('./secret.js');
 
// initialize express
var app = express();
 
// a friendly little route
app.get('/', function(req, res) {
  
  // connect to carto
  var client = new carto({
    user:secret.USER, 
    api_key:secret.API_KEY
  });
 
  var outputRows = function(err, data) {
    console.log(data.rows);
    res.send(data.rows);
  };
 
  // build your query
  // replace YOURTABLE with, well, your table
  client.on('connect', function() {
    client
    .query("select * from YOURTABLE limit 5", outputRows);
  });
    
  client.connect();  
 
});
 
// start listening
app.listen(3333);
console.log('Boom');