eventObject.js

// object that emits changed events
// when watched fields are changed

var events = require('events'),
  util = require("util");

//var myObj = new EventObject("fields", "to", "watch")
// doc = myObj.doc
// myObj.on("set", function(field){console.log("changed", field)})
// doc.watch = "foo"
// #> changed watch

var EventObject = module.exports = function() {
  events.EventEmitter.call(this);
  this.doc = makeObjectWatchingFields(this, Array.prototype.slice.apply(arguments))
};

util.inherits(EventObject, events.EventEmitter);

function makeObjectWatchingFields(ee, fields) {
  var obj = {}, values = {};
  fields.forEach(function(field){
    Object.defineProperty(obj, field, {
      get: function(){ return values[field]; },
      set: function(value){
        values[field] = value;
        ee.emit("set", field)
      }
    });
  })
  return obj;
}