Contact list app initialization and database connection

server.js

var express = require("express");
var path = require("path");
var bodyParser = require("body-parser");
var mongodb = require("mongodb");
var ObjectID = mongodb.ObjectID;

var CONTACTS_COLLECTION = "contacts";

var app = express();
app.use(express.static(__dirname + "/public"));
app.use(bodyParser.json());

// Create a database variable outside of the database connection callback to reuse the connection pool in your app.
var db;

// Connect to the database before starting the application server. 
mongodb.MongoClient.connect(process.env.MONGOLAB_URI, function (err, database) {
  if (err) {
    console.log(err);
    process.exit(1);
  }

  // Save database object from the callback for reuse.
  db = database;
  console.log("Database connection ready");

  // Initialize the app.
  var server = app.listen(process.env.PORT || 8080, function () {
    var port = server.address().port;
    console.log("App now running on port", port);
  });
});

// ***************************************** CONTACTS API ROUTES *****************************************

Great Thanks.
I'm curious to know if you want to separate api routes in different file, e.g. api.js. how can you reuse db in that api.js??