server.js

var express = require("express");

var app = express.createServer();

app.get("/", function(req, res, next) {
  setTimeout(function() {
    next(new Error("OH NO"));
  }, 10);
});

app.error(function(err, req, res, next) {
  console.log("In the error handler");
  // you cant pass req/res, only err
  next(err);
});

app.listen(3000);