SO Question re callbacks

index.js

var models = require("../models");

exports.events = function(req, res) {
  var Edm = models.Edm;

  if (req.query.event) {
    if (req.query.campaignguid) {

      var list_id;
      Edm.find({where: {campaignguid: req.query.campaignguid}}).success(function(edm) {

        list_id = edm.id;

        switch (req.query.event) {
          case 'processed':
            increment_counter(req.query.event, list_id, function(err, retval) {
              console.log("return value is " + retval);
              res.writeHead(200);
              res.end();
            })
            break;
        }
      });
    } else {
      if (req.query.userguid) {
        console.log("userguid is present");
      }
    }
  } 
}

function increment_counter(field, id, callback) {
  var Edm = models.Edm;
  Edm.find(id).success(function(edm) {
    edm.increment(field, 1).success(function(e) {
      console.log("incremented the field!");
      return callback(null, e.processed);
    });
  })
}