Observable object properties in javascript

index.js

/**
 * A quick proof-of-concept of observable objects using JS accessors
 *
 * Base observable objects are created with * `new Observable(names)`, where
 * `names` is an array of property names that should be observable.
 *
 * Instances are created by calling .create(initial_data) on the resulting
 * base object, and observed with their .observe(handler) method. See the bottom
 * of this file for an example.
 */
Observable = function (props) {
	this.__props = props
	this.__observers = []
}

function installProperty (name, changes) {
	var _val
	Object.defineProperty(this, name, {
		get: function () { return _val },
		set: function (val) {
			if (val === _val) return;
			// store the original value
			if (typeof changes[name] === 'undefined') {
				changes[name] = _val;
			}
			_val = val;
		}
	})
}

Observable.prototype.observe = function (observer) {
	if (this.__observers.indexOf(observer) !== -1) return
	this.__observers.push(observer)
}

Observable.prototype.create = function (init_data) {
	var previous = {}
	var self = new this.constructor(this.__props)
	for (var _ in this.__props) {
		installProperty.call(self, this.__props[_], previous)
	}
	if (init_data) {
		for (var key in init_data) {
			self[key] = init_data[key]
		}
	}
	var notifyObservers = function () {
		var changes = []
		for (var k in previous) {
			if (self[k] !== changes[k]) {
				changes.push([self, k, self[k], previous[k]])
			}
			delete previous[k]
		}
		for (var i in changes) {
			for (var j in self.__observers) {
				self.__observers[j].apply(null, changes[i])
			}
		}
		process.nextTick(notifyObservers)
	}
	process.nextTick(notifyObservers)
	return self
}

// Usage

var Person = new Observable(['name'])
var joe = Person.create({name: 'Joe'})

function observer (instance, key, newVal, oldVal) {
	console.log({
		isJoe: person === joe,
		key: key,
		oldVal: oldVal,
		newVal: newVal
	})
}

joe.observe(observer)

joe.name = 'Joey J'

process.nextTick(function () {
	joe.name = 'observer will never see this state'
	joe.name = 'Joseph'
})