observable with computed fields

example.js

var Model = require('./')

var m = new Model()
var n = new Model()

n.compute('change', function (time, name) {

  return 'changed name to:' + name + ' at ' + time

}, [ [m, 'time'],  'name' ])

n.on('change:change', console.log)


setInterval(function () {
  m.set('time', new Date())
}, 233)

setInterval(function () {
  n.set('name', Math.random() < 0.5 ? 'jim' : 'bob')
}, 533)

index.js

var EE = require('events').EventEmitter
var inherits = require('util').inherits

module.exports = Model

inherits(Model, EE)

function Model () {
  this._store = {}
  this._localStore = {}
}

var m = Model.prototype

m.set = function (key, value) {
  this._store[key] = value
  this.emit('change', key, value)
  this.emit('change:'+key, value)
  return this
}

m.setLocal = function (key, value) {
  this._localStore[key] = value
  this.emit('change', key, value, true)
  this.emit('change:'+key, value, true)
  return this

}

m.get = function (key) {
  return this._localStore[key] == null ? this._store[key] : this._localStore[key]
}

function isObservable (o) {
  return (
    o
  && 'object' === typeof o
  && 'function' === typeof o.on
  && 'function' === typeof o.get
  )
}

m.compute = function (name, func, attrs) {
  var args = new Array(attrs.length), set = new Array(attrs.length)
  var self = this
  var _update = false

  function key(i, v) {
    args[i] = v
    set[i] = true
    update()
  }

  function update() {
    if(_update) return
    _update = true
    process.nextTick(function () {
      _update = false
      var l = set.length
      while(l--) //wait until all the args are ready to go.
        if(!set[l]) return

      self.setLocal(name, func.apply(self, args))
    })
  }

  attrs.forEach(function (attr, i) {
    if('string' === typeof attr)
      self.on('change:'+attr, function (val) {
        key(i, val)
      })
    else if(isObservable(attr))
      attr.on('change', function (val) {
        key(i, attr)
      })
    else if(Array.isArray(attr)) {
      console.log('AARY', attr)
      attr[0].on('change:'+attr[1], function (val) {
        key(i, val)
      })
    }
  })
}